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Form 1220-5 

Haniiflrv 1 Q7A\ 
BLM LIBRARY 




TECHNICAL NOTE 



Filing Code 6611 

Date Issued October 1980 

Technical Note # 344 



U.S. DEPARTMENT OF THE INTERIOR - BUREAU OF LAND MANAGEMENT 



THE COMMON RAVEN 



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no. 344 


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by Richard L. Knight 
Mayo W. Call 




Additional copies of Technical Notes are available from DSC, Federal Center Building 50, Denver, Colo., 80225 



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THE COMMON RAVEN 



by 



Richard L. Knight 

Washington Department of Game 

Olympia, Washington 



and 



Mayo W. Call 
Bureau of Land Management 
Denver Service Center 
Denver, Colorado 






^au of Land Management 
ary 

leral Center 
J 8Q225 



For sale by the Superintendent o( Documents, U.8. Government Printing Office, Washington, D.C. 20402 



TABLE OF CONTENTS 

Page 

INTRODUCTION 1 

SPECIES DESCRIPTION 3 

DISTRIBUTION: PAST AND PRESENT 4 

STATUS AND POPULATION TREND 6 

LIFE HISTORY 7 

Reproduction 

Courtship and Territory Occupancy 7 

Nest Building 7 

Nest Defense 9 

Nesting Period 10 

The Young Raven 12 

Productivity 14 

Food Habits 16 

Hunting Methods 18 

Vocalizations 19 

Social Behavior 20 

Roosting 21 

HABITAT REQUIREMENTS 23 

Factors Involved in Nest Site Selection 23 

Nest Sites 25 

Territory Size 28 

INTERSPECIFIC RELATIONSHIPS 32 

LIMITING FACTORS 35 

Nesting Sites 35 

Food 35 

Human Disturbance 36 

Logging 37 

Chemical Contamination 37 

ECONOMIC CONSIDERATIONS 39 

SPECIES AND HABITAT MANAGEMENT RECOMMENDATIONS 41 



Page 

PROTECTIVE MEASURES INSTITUTED 43 

RESEARCH TECHNIQUES 44 

ONGOING RESEARCH PROJECTS 51 

AUTHORITIES 52 

ORGANIZATIONS ACTIVELY INVOLVED WITH THE WELFARE OF RAVENS . 53 

LITERATURE CITED 54 

PHOTO CREDITS 61 



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INTRODUCTION 



Throughout the centuries, the raven has captured the imagination 
of people from all walks of life. Conner et al. (1976) stated that 
"when the calls of the raven pierce the dawn they engender all that is 
wild and free. '* The raven has long been considered a symbol of 
wilderness. From earliest times, innumerable legends, stories, and 
beliefs have been built around the bird. Ravens are not only con- 
spicuous, but amazingly intelligent. It is, therefore, not surprising 
that they have often figured in folklore, legends, and literature. 
Goodwin (1976) discussed how the raven, with its black plumage, harsh 
voice, and carrion-eating habits, left a strong impression on early 
civilizations. 

Sprunt (1956) suggested that a certain fear and animosity toward 
the raven existed in remote areas of the Blue Ridge Mountains settled 
by Anglo-Saxons. Their attitude toward the raven had, no doubt, been 
handed down from generation to generation. In Norse mythology, the 
raven was sacred to the god Odin, whose two ravens, Thought and 
Memory, flew about the world all day and at evening returned to their 
master to tell him what was going on. The raven was also used as a 
land-finder by sea-going people. According to folklore, Iceland was 
first discovered in this manner (Goodwin, 1976). 

In much of western Europe, including the British Isles, the raven 
acquired a reputation as a bird of evil omen. This was partially due 
to its association with Viking raiders who carried with them emblems 
of the raven. 

To the Alaskan and Canadian Coast Indian tribes, the raven was 
considered a hero, recognized by all, yet having many different names. 
The Tlinget called it Yel, while it was Txamsem to the Tsimshian 
Tribe. On Vancouver Island, it was called Meskwa, the Greedy One, but 
to the Bellabella, it was Hemaskas, Real Chief. The Haida called the 
raven Nankislas, He Whose Voice is Obeyed, and used it as one of their 
two main crests (Ayre, 1961). The Rivers Inlet Tribe knew it as 
Kwekwaxawe, Great Inventor, while the Tahltan Tribe called it Sketco, 
Great Raven. 

To those many and diverse tribes of the northern Pacific Coast, 
the raven was portrayed more often, and in more ways, than any other 
creature of legend. It was Raven the transformer, the trickster, the 
Big Man who created the world; put the sun, moon, and stars in the 
sky; the fish in the sea; salmon in the rivers; and food on the land. 
He manipulated the ocean tides to assure daily access to beach 
resources, and gave the tribes fire and water, placed the rivers, 
lakes, and cedar trees over the land, and peopled the earth (DeArmond, 
1975^- 



These early people believed the ra^en was capable of turning 
itself into anything at any time. It could dive beneath the sea, 
ascend into the sky, or make things happen merely by willing it. Its 
behavior was often motivated by greed, and it took great pleasure in 
teasing, cheating, and tricking, although all too often the tables 
were turned on it (DeArmond, 1975). 

Today, the raven finds itself in an equally perplexing position. 
Accused of being either highly destructive or economically important, 
it nevertheless has attracted an ever increasing following of people 
who admire it for its intelligence, beauty, and interesting behavior. 

Stewart Janes (1980, pers. comm.) described the raven in this 
way: "First, I will say that I have found ravens to be the roost 
exasperating birds to work with. They are indistinguishable as 
individuals, essentially non-territorial, masters at concealing nests, 
and in general, smarter than man." 

This Technical Note has been prepared to give a better under- 
standing of this bird, not so much for its unique place in history and 
legend, as for its role in living systems and its relationship to 
raptors and other important wildlife. It frequently competes directly 
for food with several species of raptors, often killing small rodents 
to eat and robbing eggs and young from other birds' nests. On the 
other hand, its nests are, often used by owls and other raptors as 
their own platforms, without which they might be unable to nest in 
some areas. 

The raven is a complicated species, with many complex inter- 
relationships with other wildlife and with man. It is hoped that this 
publication will provide an insight into its life, habits, and both 
the beneficial and adverse influences on the lives of various kinds of 
wildlife and on man. 




SPECIES DESCRIPTION 



There are three subspecies of common raven: Corvus corax 
principalis , Corvus corax sinuatus , and Corvus corax clarionensis . 
Oberholser (1918) considered the raven subspecies to be almost wholly 
without differences in size and proportion. Willett (1941) noted 
several factors that make it difficult to recognize differences in the 
subspecies, including color similarity and individual variation in 
size within the same region (often so great that even a fairly large 
series of specimens obtained at random may be misleading). Since 
little information exists on migratory movements, it is unsafe to 
assume that birds taken outside the breeding season are members of the 
breeding population where they were secured. Only size and proportion 
are useful in distinguishing races. 

Willett (1941) considered C. c_. principalis , with its heavy bill 
and tarsus, to be the largest subspecies. C_. c_. sinuatus is also 
large, but has a slender bill and tarsus. C^. c^. clarionensis is the 
smallest of the three subspecies. 

The common raven is the largest all-black species in family 
Corvidae in the world (Goodwin, 1976), being 30 to 50 percent larger 
than the common crow ( Corvus brachyrhynchos ) . In flight, ravens can 
be distinguished from crows not only by the larger size, but by the 
fact that a raven's tail is wedge-shaped while the crow's tail is 
typically quite round (Conner et al., 1976). 

Kerttu (1973) developed aging techniques for the common raven and 
proposed three age classes. During the hatching year, the soft palate 
is pink to spotted, the iris is gray to half brown, and the dull 
plumage is initially smooth with much wear of primaries after half a 
year. Second year birds have soft palates that are light pink to gray 
in color, the iris is half to completely brown, and the plumage is 
progressively molted during the summer into adult coloration. Third 
year and older birds have dark mouths, a brown iris, and metallic 
black plumage. The molt occurs from June to December with little wear 
in flight feathers. Murray (1949) reported a sighting of an all-white 
raven by woodcutters in the Blue Ridge Mountains during the 1940 's. 



DISTRIBUTION: PAST AND PRESENT 



The common raven is a holarctic species that is found from sub- 
arctic Alaska through northern Canada, and south through the western 
United States and Mexico. It is also found in central and eastern 
North America, including Minnesota, Wisconsin, northern Michigan, 
central Ontario, southern Quebec, and Maine, and south from the 
Appalachian Mountains to northwestern Georgia (Kerttu, 1973; Fig. 1). 

Historically, Dickey (1915) described the raven's range in the 
eastern United States as the Alleghany Mountains of northern Georgia 
to the Adirondack Mountains of northern New York and the mountains of 
parts of New England. In the lowlands, the birds were sometimes found 
on the Virginia and New Jersey coasts. Dickey (1915) considered them 
to be most abundant on the Maine Coast. In the interior, ravens were 
found nesting in the mountains of central Pennsylvania and on the 
higher ridges of Virginia, West Virginia, Kentucky, and North 
Carolina. 

Within the past century, the raven was eliminated from Alabama 
and Kentucky (Hooper, 1973). Prior to 1875, ravens were present 
throughout the breeding season across the Canadian prairie provinces, 
extending down into the Dakotas. The disappearance of the raven in 
this area was attributed to widespread use of baited traps, poisons, 
and the disappearance of the buffalo (Hooper, 1973; Houston, 1977). 
Jollie (1976) attributed the disappearance of the raven in the midwest 
to the clearing of forests and the conversion of land to agriculture. 

Recently, the raven has been reinvading the historic range and 
colonizing new areas. White et al. (1975) observed ravens nesting on 
the Coastal Plains in Alaska in 1974, the first reported nesting that 
far north. They believed that the presence of people and oil pipeline 
work camps provided food resources that enabled ravens to extend their 
breeding range northward. In 1977, Eustis (1978) saw a pair of nest- 
ing ravens in southern Michigan, which was the first confirmed raven 
nest in that area since the big logging era in the 1800' s. Howe 
(1978) reported ravens being seen in northeastern United States 
localities where they had not been seen for decades. Ravens have also 
recently been seen in Massachusetts, northern New Jersey, eastern 
Pennsylvania, southeastern Kentucky and Ontario, and in the northern 
Sierras of California, where they were formerly rarely seen. 







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STATUS AND POPULATION TREND 



The common raven was offered complete protection in 1974 by the 
U.S. Fish and Wildlife Service due to an international agreement with 
Mexico. The common raven is considered to be a resident species over 
most of its range, although some wandering and local migration of 
immature and non-breeding birds does occur (Sprunt, 1956; White and 
Cade, 1971; Goodwin, 1976). 

The common raven was considered a fairly common breeding bird as 
late as the early 1900' s in the southern Appalachian Mountains from 
northern Pennsylvania to northern Georgia (Bendire, 1895; Harlow, 
1922; Murray, 1949; Sprunt, 1956). Harlow (1922) and Sprunt (1956) 
attributed the decline to persecution by humans, largely due to super- 
stitious ignorance. The raven, however, is apparently extending over 
much of its former range in the Appalachians, including along the 
coast in the middle and southern Atlantic states (Sprunt, 1956) where 
it historically occurred (A.O.U., 1957). This increase is attributed 
to less shooting of the birds by man, creation of the Great Smokey 
Mountain National Park, and a greater abundance of food (scraps) left 
at camps and picnic grounds by tourists on the Blue Ridge Parkway 
(Murray, 1949; Sprunt, 1956; Hooper, 1977). 

In the Upper Peninsula of Michigan, the raven was considered 
common prior to the 1900' s. Barrows (1912) indicated a population 
decline, and Leopold in 1938 (Anon. , 1967) felt the raven was becoming 
less common and deserved special protection in Michigan. In the 
mid-1950 1 s, however, DeVos (1964) considered the raven to be in- 
creasing in range and numbers and attributed the increase to a greater 
number of highway animal kills. 

The number of common ravens is generally thought to be increasing 
in the West and in Alaska for a variety of reasons. Frank C. Craig- 
head, Jr. (1980, pers. comm.) observed a 366 percent increase in 
ravens within a 12 square mile area at Moose, Wyoming between 1947 and 
1975. Houston (1968) suggested that an abundant artificial food 
source provided by park service garbage dumps might be maintaining an 
artificially high raven population. McBee (1937), White and Cade 
(1971), and Ferguson et al. (1976) mentioned that ravens were extend- 
ing their range and numbers by using artificial nesting structures 
such as abandoned buildings, oil derricks, and windmills. 



LIFE HISTORY 



REPRODUCTION 

Courtship and Territory Occupancy 

Common ravens show great fidelity to nesting sites. Ratcliffe 
(1962) found raven populations in England to be stable from year to 
year, and White and Cade (1971) described active raven nesting sites 
in Utah that had been occupied as early as the 1920' s. Smith and 
Murphy (1973) found that the raven showed the greatest population 
stability on their Utah study area, with four pairs of ravens 
occupying their respective territories for four consecutive years. 
Bendire (1895) mentioned that ravens became attached to a nesting 
sight and nested there each year even though their eggs or young were 
taken away during successive seasons. Ratcliffe (1962) observed that 
nesting cliffs would often remain occupied in successive years even 
after being robbed or destroyed annually. In Virginia, Murray (1935) 
reported that nesting cliffs are used year after year and that one 
nest was visited every year for 11 years without driving the birds 
away. Jones (1935) reported that a pair occupied the same cliff for 
14 years. 

Mating generally occurs among ravens during the second or third 
year. Pairs tend to stay away from other ravens throughout the year 
(Jollie, 1976), although they may frequent communal roosts in the late 
fall and winter months (Conner et al. , 1976). They mate for life, 
possibly because of this real or relative isolation, although Jollie 
(1976) believed that exchange of mates occurs more often than is 
reported in the literature. Both Lorenz (1970) and Jollie (1976) 
observed that some raven pairs were "happier" than others and attri- 
buted this to their individualistic behavior. Tufts (1916) shot the 
female of a nesting pair in Nova Scotia, and within 10 days, the male 
had a new mate and had continued nesting. 

Courtship displays begin in February (Harlow, 1922; Zirrer, 1945; 
Dorn, 1972; Brown, 1974). This consists of pursuit flights, aerial 
maneuvers, mutual feather preening, and strutting. Lorenz (1970) 
described the strutting display as: the head held high, "ears" 
raised, throat puffed out, wings slightly spread from the body, belly 
feathers extended down and laterally below the wings, and tail 
slightly fanned. Dorn (1972) observed that both members of a pair 
usually strut simultaneously. 



Nest Building 

There is a difference of opinion about whether ravens reuse a 
nest. Jones (1935) stated that no part of the previous year's nest is 



used again the following year, whereas Stiehl (1978) observed ravens 
using the same nest for several years. He was unable to detect a 
correlation between nesting success and reuse of a nest. Of eight 
identifiable pairs of ravens observed in 1967 and 1977, four pairs 
used the same nests both years, and four pairs changed nest locations. 
Stiehl (1978) also observed the alternating use of raven nests by 
golden eagles, red-tailed hawks, great horned owls ( Bubo virginianus ), 
and common ravens. 

Hooper et al. (1975) observed in Virginia that ravens typically 
start nest building in early February, and in Pennsylvania, Harlow 
(1922) found that nest building started between the 7th and 15th of 
February. In Wyoming, Dorn (1972) first observed nest construction on 
March 29, and Bowles and Decker (1930) observed that nest building in 
Washington frequently began in early March. 

Harlow (1922) determined that nest building takes between 14 and 
18 days, and Dorn (1972) observed a pair of ravens in Wyoming that 
spent at least 10 days constructing a new nest in an aspen ( Populus 
tremuloides ) tree. 

Harlow (1922) and Bowles and Decker (1930) both observed that 
nest building was done almost exclusively by the female, but Dorn 
(1972) and Stiehl (1978) found that both pair members participated in 
nest construction. The nests are usually large, yet well-defined 
structures that conform in contour with the ledge or crotch on which 
they are placed. Tree nests as a rule occupy the highest available 
strong crotch. 

Harlow (1922), Dorn (1972), and Stiehl (1978) provide detailed 
observations of nest construction. Large sticks are first stacked for 
a foundation with a loose basket woven about the perimeter of the 
base. Harlow (1922) observed that ravens usually break dead branches 
for the base, and that some are over 3/4 inches in diameter and 3 feet 
long. Dorn (1972) similarly noted that ravens break most of the 
sticks from trees, although occasionally a bird was observed removing 
nest material from an inactive raven nest. Twigs are broken off and 
carried to the nest with the bill. If nesting material is dropped 
enroute to or at the nest, no attempt is made to recover it. Smaller 
twigs are placed in the basket and woven into the outer framework 
until the structure is approximately eight inches deep. 

A layer of soil between 0.4 and 1.1 inches deep is formed at the 
bottom of the basket. It is not known how the soil is carried to the 
nest. The soil-bottomed stick nest is then lined with a variety of 
material, the most common being the hair of nearly anything including 
deer, sheep, cows, horses, dogs, skunks, cats, opossum, coyotes ( Canis 
latrans ) , or rabbits. It is not uncommon to find shredded bark, grass 
or moss being used. Bowles and Decker (1930) observed that raven 
nests in Washington's desert often consisted of different kinds of 



wire as well as bones. Stiehl (1978) found a coyote tail in one nest 
bowl, and Harlow (1922) observed a deer tail in another. Bits of 
paper, cloth, and clothing are also commonly found in nest bowls. 



Nest Defense 

Intraspecif ic nest defense by common ravens is usually weak. In 
Wyoming, Dorn (1972) watched flocks of ravens wander through nesting 
territories with impunity and speculated that flocks of conspecifics 
may inhibit nest defense. Nest defense against raptors, crows, and 
humans varied considerably, although the individual variation observed 
was usually constant (Dorn, 1972; Hooper, 1977). 

Dorn (1972) observed a pair of nesting ravens that often vigor- 
ously harassed a pair of red-tailed hawks nesting a quarter mile away. 
In Pennsylvania, Harlow (1922) noted that ravens easily intimidated 
red-tailed and broad-winged hawks near a nest. He also observed 
ravens harassing crows and at times driving them from sight. 

Ravens are exceedingly wary about the nest site when humans are 
nearby (Bowles and Decker, 1930; Murray, 1949). Before the eggs 
hatch, an incubating raven will normally attempt to slip off the nest 
quietly when a human approaches. After hatching, however, ravens will 
often fly overhead, calling frequently (Dorn, 1972). 

Stiehl (1978) determined two types of responses to humans near a 
nest. In areas of heavy human disturbance, he noted, ravens were quick 
to flush from a nest, whereas at nest sites with infrequent human dis- 
turbance, female ravens remained tenaciously on the nest when 
approached by humans. In Alaska, Brown (1974) had a raven dive at him 
as he was climbing the nest tree. The partly folded wings produced a 
"whissh" sound, and Brown speculated that the diving displays were 
intended to fighten off potential predators. 

Hooper (1977) observed that in 16 out of 24 nesting territories 
in Virginia, ravens evaded and were seldom vocal when humans 
approached. In the other eight territories, the birds appeared 
defensive and were highly vocal. Evasive birds usually left the nest 
vicinity and would soar within sight of the nest at distances of 1,200 
to 2,400 feet. Defensive birds uttered rapid "kack-kack" or "hark" 
calls and flew within 150 feet or less of the intruders. 

Bowles and Decker (1930) approached a nest site in Washington 
where both birds performed a remarkable display of aerial tumbling, 
then perched on the cliff 50 feet from the nest site. The ravens then 
gave a series of calls, described as "quacking like a duck" and 
"bawling like a cat". 



Both Tyrrell (1945) and Dorn (1972) observed ravens breaking tree 
branches and pecking vigorously at tree limbs when humans approached 
the nests. Tyrrell (1945) reported that one raven would break off 
twigs in its bill, shake them strongly, then drop them to the ground. 

In Oregon, Janes (1976) visited a raven nest where the pair 
"threw" rocks at the observers. The ravens picked up at least six 
rocks with their bills and "threw" them down at the two individuals. 
The largest rock was 3 inches in diameter and 1 inch thick and had 
apparently been partially buried. Subsequent visits to the nest site 
failed to provoke any further rock throwing. 



Nesting Period 

In a study of ravens in Britain, Ireland, Wales, and Scotland, 

Holyoak (1967) found that although ravens breed later farther north, 

they nest no later at higher elevations than at lower elevations at 
the same latitude. 

Several days usually elapse between the completion of the nest 
and the laying of the first egg (Dorn, 1972). Harlow (1922), however, 
observed that this period varied among individual pairs from 3 days to 
a week. 

Harlow (1922) noted that over a 3-year period, nesting ravens in 
Pennsylvania laid their eggs between February 22 and April 5, while 
Tyrrell (1945) in Shenandoah National Park, and Hooper (1977) in the 
southern Appalachians of Virginia, found eggs in most nests around the 
first week of March. 

For 4 years, Smith and Murphy (1973) found the average egg- 
laying dates of nesting ravens in Utah to be between March 27 and 
April 2, with extremes between March 19 and April 8. Dorn (1972) 
calculated the egg-laying dates of nesting ravens in Wyoming to be 
between April 7 and May 14. Over a 3-year period in the Birds of Prey 
Natural Area in Idaho, the mean egg-laying dates were between March 29 
and April 4 (Kochert et al., 1975, 1976, 1977). The earliest recorded 
egg-laying date was March 1 and the latest observed date was May 10. 

Bowles and Decker (1930) and McBee (1937) noticed that in 
Washington, complete clutches are usually found by the first week of 
April, although eggs are first laid as early as March 14, and as late 
as May 20. They also observed that if the first set of eggs is 
removed, it is not uncommon for another set, and in some cases a 
third, to be laid in the same nest. Bowles and Decker (1930) found 
that the second or third sets would often contain one egg less than 
the first. Dorn (1972) found no evidence of second clutches or 
renesting, even though three clutches were destroyed during egg-laying 
or incubation. 



10 



In Oregon, Stiehl (1978) observed an initial refractory period 
after the laying of the first egg, which was followed by the laying of 
two eggs, then an egg daily until the clutch was complete. Both 
Harlow (1922) and Bowles and Decker (1930) determined that eggs were 
laid daily until the clutch was complete. 

Ravens begin incubation after laying the first egg (Stiehl, 
1978), although Dorn (1972) speculated that true incubation may start 
gradually as the brood patch becomes more vascularized. Harlow (1922) 
also observed that during severe weather, ravens remain on the nest 
from the time the first egg is laid. Although Tyrrell (1945), Bent 
(1964) and Conner et al. (1976) observed both sexes sharing incubation 
duties, Harlow (1922), Bowles and Decker (1930), and Stiehl (1978) 
determined that only the female incubates the eggs, with the male 
providing food for the female. When not gathering food, the male will 
"stand guard" near the nest on a perch with a commanding view of the 
area (Stiehl, 1978). 

Bancroft (1927) reported that ravens in central California 
required two weeks to incubate their eggs, although others (Harlow, 
1922; Tyrrell, 1945; Dorn, 1972; Conner et al., 1976; Stiehl, 1978) 
have determined the incubation period to be approximately 21 days. 
Dorn (1972), Conner et al. (1976), and Stiehl (1978) observed that 
hatching is asynchronous, and Dorn noted that the eggs hatched at 
intervals of a day or less. Stiehl (1978) reported that almost 
invariably one egg of a clutch failed to hatch. This occurred with 
such regularity that he felt clutch size could be accurately deter- 
mined by adding one to the number of hatchlings at 7 to 10 days old. 

Smith and Murphy (1973) found that the average hatching dates of 
ravens in Utah over a 4-year period were between May 1 and May 12. The 
earliest observed hatching date was April 27, and the latest was May 
18. 

In Idaho, Kochert et al. (1975, 1976, 1977) observed that the 
average hatching date over 3 years varied between April 26 and May 4, 
with the earliest observed hatching date being April 12, and the 
latest being May 28. 

Hooper (1977) reported that ravens in Virginia fledged in late 
April and early May. Harlow (1922) observed in Pennsylvania that 
ravens can fly short distances from the nest after 4 weeks, but Conner 
et al . (1976) noted that they left the nest when 6 to 7 weeks old. 

In Wyoming, Dorn (1972) noted an average of 42 days between the 
hatching of the first egg and the fledging of all surviving young in a 
nest. The range was 39 to 45 days. In Oregon, Stiehl (1978) deter- 
mined that ravens fledged at about 41 days of age. 



11 



Smith and Murphy (1973) determined the average brood departure 
dates in Utah over 4 years to be between May 7 and June 12. The 
earliest brood departure date observed was May 3, and the latest was 
June 23. At the Birds of Prey Natural Area in Idaho, Kochert et al. 
(1975, 1976, 1977) observed the average fledging dates to be between 
June 1 and June 3, with some fledging as early as May 12, and others 
as late as July 9, which was a renesting attempt. The latest date at 
which young were still seen near the nest site over a 3-year period 
was August 6. This gave a breeding season of 197 days. 

Dorn (1972) observed that after fledging, adults continue to 
feed the young for at least a week, with some family groups together 
for a month after fledging. The nest site remains a center of 
activity until mid-July for most ravens in the Harney Basin, Oregon, 
at which time a change in food availability or preference alters that 
location (Stiehl, 1978). Stiehl (1978) observed two distinct 
post-fledging patterns, depending on whether the nesting attempt was 
early or late. When the nesting attempt was early, the post-fledging 
period averaged approximately 6 weeks, whereas when the nesting 
attempt was made late in the season, the post-fledging period was 
compressed to about a week. 



The Young Raven 

In Oregon, Stiehl (1978) observed that any unhatched eggs remain 
in the nest from 4 to 7 days after the hatch of the clutch, and 
speculated that the adult ravens consumed the eggs. Gwinner (1965) 
reported that ravens remove and eat eggshells of any unhatched eggs. 

When ravens are born, they are naked, orange in color, and 
sightless. Stiehl (1978) was unable to elicit response to calls from 
ravens at 1 day post-hatch, but at 3 days, the same calls elicited a 
begging behavior. At about one week old, the young are still naked, 
but have doubled in size, and their eyes are functional at 12 to 14 
days (Conner et al. , 1976; Stiehl, 1978). 

Stiehl (1978) noted that young ravens are most vulnerable to 
predation during the first 2 weeks after hatching, during which 71 
percent of the dated nest depredations occur. Dorn (1972) and Kochert 
et al. (1975, 1976) determined that most raven mortality occurs 
before or during incubation, primarily because of hatching failures 
and nest abandonment. In New Mexico, Mishage (1974) determined that 
most nesting mortality of white-necked ravens ( Corvus cryptoleucus ) 
occurs during the initial one-third (less than 16 days) of the 
nestling period and attributed it to starvation and human disturbance. 

Stiehl (1978) reported that young ravens over 14 days of age 
remain silent in the nest when approached. He surmised that the high 



12 



mortality rate during the first 2 weeks may be the result of 
indiscriminate vocalizations by the blind young which could have 
attracted predators. 

In Wyoming, Dorn (1972) observed that parents brood the young 
almost continuously during the first few days after hatching and then 
continue to brood their young for at least 2 more weeks. Brooding 
attentiveness decreases over time, and Dorn never observed adults 
brooding their young during the day at 25 to 28 days of age. In 
Idaho, Kochert et al. (1977) observed that the female broods the 
young, and that brooding was not observed after the young were more 
than 23 days old. 

Kochert et al. (1977) found that females performed 72 percent of 
183 observed nest maintenance visits. Nest maintenance consists of 
carrying off fecal sacs, casts, and discarded food. The female also 
probes and fluffs the nest. 

Dorn (1972) noted that both parents feed the nestlings by 
regurgitation, bringing only enough food for one nestling on each nest 
visit. Older nestlings were fed every 3 to 5 minutes during one 
morning observation period, while younger nestlings were fed only once 
during a one-and-a-half hour morning observation period. Kochert et 
al. (1977), in their definitive study of raven nest behavior, observed 
adult ravens visiting nests to feed young an average of 50.9 times a 
day, with no observed correlation between feeding frequency and time 
of day or stage of brood-rearing. An average of 1.5 young were fed 
per visit. They did observe that some of the young were fed more than 
others, but not significantly more. Mishage (1974) noted that 10 out 
of 11 starved white-necked raven nestlings were either the youngest or 
next to the youngest, indicating that discriminate feeding and/or the 
ability to compete for food does exist. 

At about 30 days of age, young ravens become more active in the 
nest. During the last week in the nest, Dorn (1972) observed that 
increased activity caused the nests to gradually disintegrate, and the 
young frequently moved from the disintegrating nests to adjacent tree 
limbs before they could fly. Stiehl (1978) noted that sustained 
flight was impossible for young ravens, and even short flights were 
difficult and usually followed by frequent calls, gaping, and panting. 

Dorn (1972) found that adults continue to feed fledged young for 
at least a week, and Kochert et al. (1977) noted that individual 
broods of ravens are usually not found near the nest site any longer 
than 2 weeks after fledging. They noted that although ravens did move 
as a group out of the canyon, they did not necessarily remain in 
family units. In Wyoming, Dorn (1972) observed family groups still 
together a month after fledging and noted that the young of the same 
brood often fed and loafed together at a dump site. 



13 



Productivity 

Ravens in Europe are unique in that they show a decrease in 
clutch size from the south to the north (Holyoak, 1967). Smith and 
Murphy (1973) in Utah observed that raven clutches varied from three 
to seven eggs and averaged 5.35 eggs over four nesting seasons. Dorn 
noted that the average clutch size in Wyoming was 5.4 eggs, with a 
range of three to six eggs. In Oregon, Stiehl (1978) observed an 
average clutch size of 6.0 eggs in 45 nests, with clutch sizes varying 
from three to seven eggs. In the Birds of Prey Natural Area in Idaho, 
Kochert et al. (1975, 1976, 1977) noted that mean clutch size varied 
from 5.08 to 5.30, and clutch size again varied from three to seven 
eggs. 

Kochert et al. (1977) reported that 54 percent of the eggs 
hatched in nests for which both the clutch size and the number hatched 
were known, but noted that since ravens clean their nests of unhatched 
eggs, it is difficult to assess embryonic mortality. During a 3-year 
period, Kochert et al. noted that raven reproductive losses were 
greatest during incubation, with hatching failures and nest abandon- 
ment being the greatest causes. Of 54 eggs that did not hatch, 20 
disappeared from nests prior to the hatching date, 25 failed to hatch 
from undetermined causes, and 9 were abandoned. 

In Utah, Smith and Murphy (1973) observed that between 1967 and 
1970, ravens successfully hatched 70.5 percent of all their eggs. 
They noted that nest desertion was observed in every raptor species in 
their study area, with the exception of the raven and Cooper's hawk 
( Accipiter cooperii ). In Wyoming, Dorn (1972) determined that nesting 
mortality occurred before or during hatching, and that hatching mor- 
tality was 35 percent. 

Stiehl (1978) noted that in Oregon, almost invariably one egg of 
a clutch failed to hatch. During a 2-year period, 69 to 71 percent of 
the eggs in all clutches hatched. 

In 1975 and 1976, in the Birds of Prey Natural Area in Idaho, 
Kochert et al. (1975, 1976) found that the maximum hatching ravens per 
nesting attempt averaged 3.30 to 3.66, with /a range of from to 7. 
In 1977, Kochert et al. noted that the number of hatchlings per 
breeding attempt was 3, with the mean brood size among nests that 
hatched young being 4.8. Stiehl (1978) noted that in Oregon the 
average brood size of 51 nests during a 2-year study was 4.2, with a 
range of from to 6 young. 

In Virginia, Hooper et al. (1975) observed that an average of 2.5 
young fledged in 35 nesting attempts where the outcome was known. In 
Wyoming, Dorn (1972) determined that an average of 1.67 young fledged 
per nest from 24 nests where the outcome was known. In 10 of these 



14 



nests, no young fledged, and no more than 4 young fledged from any one 
nest. Smith and Murphy (1973) noted that in their Utah study area, 
ravens averaged 2.57 young fledged per nest over a 4-year period. 

Kochert et al. (1975, 1976, 1977) probably have the most complete 
information on the fledging of common ravens. In Idaho, they found 
that for each year during a 3-year period, ravens fledged between 2.1 
and 2.45 young per pair, 2.4 and 2.88 young per nesting attempt, and 
3.7 and 3.88 young per successful attempt. Stiehl (1978) observed 
that a mean of 2.3 young fledged per pair in 53 Oregon nests, and 
Stewart Janes (1980, pers. comm.), also in Oregon, observed that 3.3 
young fledged in 18 nesting attempts, and 3.9 fledged in 15 successful 
nests. 

Hooper et al. (1975) reported that of 35 nesting attempts in 
Virginia, 63 percent fledged young. In Wyoming, Dorn (1972) 
calculated that the nestling survival of 14 nests, for which both 
clutch size and number of fledgings were known, was 19 percent, 
although she felt the actual value was higher. She noted that of 
seven nests that failed after hatching, four failed before the young 
were 2 weeks old. Possible predators included hawks, other ravens, 
owls, and martens ( Martes americana ). She observed that in areas 
frequented by flocks of non-breeding ravens, no raven nests were 
successful. The mortality rate continued to increase as nestlings 
became older. One young died when it was approximately 4 1/2 weeks 
old. The dead nestling was not removed from the nest. Holyoak (1967) 
observed that in England ravens also failed to remove large, dead 
young from the nest. 

Smith and Murphy (1973) determined that the overall fledging 
success of ravens for 4 years in Utah was 47.4 percent. This varied 
from a low of 40.9 percent in 1969 to a high of 57.1 percent in 1967. 

During three years at the Snake River Birds of Prey Area in 
Idaho, Kochert et al. (1975, 1976, 1977) noted that between 5 and 11 
percent of the adult population did not breed. Nesting success over 3 
years averaged between 63.0 and 71.1 percent per pair and 74.0 and 
78.0 percent per attempt. In 1977, nestling survival at eight nests 
was 69 percent. Of 40 nestling mortalities over 3 years, 15 died as a 
result of human disturbance, 13 disappeared from nests prior to the 
expected fledging date, 7 died of unknown causes, 4 died from 
predation, and 1 died following the death of a parent. 

Stiehl (1978) noted that of 85 nesting attempts during a 2-year 
period in Oregon, 60 percent were successful in fledging one or more 
young. Of 34 nesting failures, 20 were the result of depredation, 7 
were attributed to insufficient food supply, 5 were due to human 



15 



disturbance, and 2 occurred where the nests had fallen from their 
locations. Seventy-four percent of the hatched young fledged. Stiehl 
noted that most predation occurred within a week of hatching, although 
two nests were destroyed at 35 days after hatching. Coyotes, rac- 
coons, weasels ( Mustela spp . ) , great horned owls, and humans were 
suspected as being primarily responsible for nest depredations. 



FOOD HABITS 

The common raven is adapted to widely scattered and limited food 
supplies (Jollie, 1976) as well as to a broad spectrum of foods (White 
and Cade, 1971). Tyrrell (1945) described the raven's food as any- 
thing edible, alive or dead, that it can catch, kill, disable, or pick 
up. Its diet is no doubt almost as varied as that of the crow, of 
which the greater part is carrion, with small mammals next in impor- 
tance. Stewart Janes (1980, pers. comm.) observed in Oregon that 
different pairs of ravens have distinct diets, with some leaning 
heavily toward a vegetarian diet, others being scavengers, and some 
being successful predators, living on Belding ground squirrels 
( Citellus beldingi ) and weasels ( Mustela spp . ). 

Bendire (1895) described ravens as feeding principally on 
carrion, dead fish and frogs, insects, worms, mussels, snails, and 
small rodents, as well as on refuse from kitchens and slaughterhouses. 
They have also been seen feeding on the seeds of poison oak ( Rhus 
diveratola ), the hulls of wild oats ( Avena fatua ) (Hoffmann, 1920), 
and on cactus fruits in California (Ross, 1925); capturing chickens in 
New Brunswick (McManus, 1935); feeding on scraps at logging camps on 
Vancouver Island (Pearse, 1938); eating Mormon crickets (Anabrus 
simplex ) in Utah (Knowlton, 1943), and water insects, small fish, 
amphibians, grasshoppers and mice in Wisconsin (Zirrer, 1945). During 
July in Michigan, ravens have been seen eating blueberries (Mahringer, 
1970), and have reportedly eaten ptarmigan ( Lagopus spp .) and 
microtines in Alaska (White and Cade, 1971). 

Larsen and Dietrich (1970) reported 35 lambs lost to a single 
pair of ravens in Oregon during 1 week. McBee (1937) commented that 
although ravens in Washington were accused of killing lambs, he had 
never heard sheepmen complain of losing any. 

Many authors have commented on the importance of carrion to 
ravens, particularly during times of food stress, such as during the 
winter season (Feilden, 1909; Nelson, 1934; Mylne, 1961; Ratcliffe, 
1962; Brown, 1974; Temple, 1974; Harlow et al., 1975; Stiehl, 1978). 
White and Cade (1971) speculated that in arctic Alaska, ravens may be 
seasonally heavily dependent on gyrfalcons ( Falco rusticolus ) for 
carrion killed by ptarmigan. Turcek and Kelso (1968) observed ravens 



16 



in captivity storing pieces of carrion and bones, indicating that wild 
birds are also capable of caching food, a highly desirable trait for 
any vertebrate that at times is dependent on a variable food source. 

Several major studies of raven food habits have been conducted in 
different parts of North America. Harlow et al. (1975) analyzed 435 
castings of ravens in Virginia and determined they are primarily 
scavengers on opossums ( Didelphis marsupialis ) , domestic sheep, deer 
( Odocoileus virginianus ) , and rabbits ( Sylvilagus spp . ) , and are 
predatory on small mammals such as mice, moles, and shrews. Dumps and 
roadways provide a regularly used supply of food. 

In Jackson Hole, Wyoming, Dorn (1972) found that ravens are both 
scavengers and predators, with their diet reflecting the availability 
of food. During the winter, ravens feed mostly at garbage dumps and, 
to a lesser degree, on carcasses of moose ( Alces alces ), elk ( Cervus 
canadensis ) , and deer ( Odocoileus hemionus ). Non-breeding flocks of 
ravens continue to feed at the garbage dumps during the summer, while 
nesting birds feed mainly on small mammals (75 percent of 111 pellets 
from 12 nest sites) such as Microtus spp . and Citellus spp . Insect 
remains and pieces of eggshells were found in only eight (7 percent) 
of the pellets. 

Kochert et al. (1976), at the Birds of Prey Natural Area in 
Idaho, observed that Townsend ground squirrels ( Spermophilus 
townsendi ) comprised 93 and 70 percent of nesting ravens' food biomass 
in 1975 and 1976, respectively. Young ravens were observed consuming 
large numbers of beetles and scorpions. In 1977, adults were observed 
delivering remains of desert horned lizards ( Phrynosoma platyrhinos ), 
side-blotched lizards ( Utah stansburiana ), and snakes to raven 
nestlings (Kochert et al., 1977). Red meat (presumably carrion) was 
delivered during 72 of 1,284 (5.6 percent) nest visits. 

In the eastern Great Basin Desert of Utah, Smith and Murphy 
(1973) found in 1969 and 1970 that nesting ravens relied heavily on 
mammals, which comprised 55.1 percent of the prey and 96.2 percent of 
the total prey biomass. Lagomorphs ( Lepus calif ornicus and Sylvilagus 
spp . ) comprised 23.9 percent of the prey and 93.2 percent of the total 
prey biomass. Almost two-thirds of the jackrabbits were immatures or 
juveniles, indicating that some were taken as carrion. Birds 
comprised 11 percent of the prey, but only 1.9 percent of the total 
prey biomass. Dermestids and unidentified beetles were the most 
frequently taken invertebrates. 

In Harney Basin, Oregon, Stiehl (1978) analyzed 2,202 food items 
found in castings of nesting birds. Mammals, mainly Lepus spp . and 
Microtus spp. , were the most important food items, with avian eggs 



17 



being second, and avian parts (feathers, down and body parts) being 
third. During late July through September, it appeared that grass- 
hoppers ( Melanoplus spp . ) were the dietary staple. 

Carrion was used in all seasons, although less in the summer 
months than at other times of the year. Stiehl (1978) observed that 
ravens seemed to prefer grasshoppers to carrion and that in late 
summer, carrion feeding increased as the number of grasshoppers de- 
creased. In October and November, ravens fed primarily in harvested 
grain fields, and carrion became increasingly important as winter 
approached. 

Stiehl (1978) believed that winter in Harney Basin was the period 
of highest food stress for ravens. Due to lower mean winter tempera- 
tures and shorter days, ravens needed more food, but had less foraging 
time. They appeared to rely more on predation during this period, but 
also used opportunistic food sources, such as cultivated grain wastes, 
dead carp, dead range animals, and placentae from cattle parturition. 

Immature, non-breeding ravens were observed feeding heavily on 
waterfowl eggs during the spring (Stiehl, 1978). A flock of 40 to 60 
ravens was often seen in prime waterfowl nesting areas and was some- 
times seen carrying eggs. 



HUNTING METHODS 

Jollie (1976) described the common raven's foraging habitat 
(other than vegetation, climate, and most other biotic factors) as 
being strongly contoured, such as along sea cliffs. 

Angell (1977) noted the advantages of the raven's black color. 
Black feathers absorb solar energy and decrease the temperature 
gradient between the skin and its outer feathers. Over a 24-hour 
period, a raven could show a net energy advantage over a non-black 
bird of comparable size. This enables ravens to live in cold areas, 
such as the Arctic, where they are able to stay year-round and take 
advantage of a continuous food supply. Its black color is also an 
advantage in extremely hot areas where it assists in a quick warming 
through solar energy absorption. This enables desert ravens to forage 
in the early morning and late afternoon and evening, hunting crepus- 
cular prey and scavenging at garbage dumps, or along a stretch of 
highway (Angell, 1977). Stiehl (1978) considers the raven to be 
primarily a sight hunter. 

In the Birds of Prey Natural Area near Boise, Idaho, Wolfe (1977) 
observed ravens foraging most often near a burned sagebrush ( Artemisia 
tridentata ) flat, an area of sparse sagebrush and croplands near the 
canyon. He also observed that ravens foraged most often in late 
afternoon and were flexible in using all types of perch sites. 



18 



Conner et al. (1975) observed ravens feeding alongside of common 
crows and starlings ( Sturnus vulgaris ) at a sanitary landfill in 
Virginia, relying on sentinal crows for warning of possible danger. 
Ravens did not enter the landfill until the sentinel crows were in 
position, and after being frightened, were the last species to return 
to the landfill to resume foraging. Conner et al. (1975) speculated 
that such a behavioral adjustment might enable ravens to more safely 
exploit a potentially hazardous food source and possibly increase 
their overwinter survival. 

Several interesting aspects of the raven's foraging behavior have 
been reported. Mallory (1977) pointed out their adaptability and 
described their feeding behavior as a learned food-gathering strategy, 
as opposed to a simple opportunistic approach. In Minnesota, Harring- 
ton (1978) observed that ravens were attracted by wolf ( Canis lupus ) 
howling during the fall and winter and theorized that ravens often 
investigate such activities for the presence of carrion. Mech (1970) 
reported ravens following wolves or wolf tracks hoping to find 
carrion. 

Montevecchi (1978) described how ravens in Newfoundland flushed 
black-legged kittiwakes ( Rissa tridactyla ) from their nests by drop- 
ping tufts of grass from above, by approaching them suddenly and 
closely while calling loudly, and even by physical attack. 

Zirrer (1945) observed ravens in Wisconsin hunting amphibians on 
foot by turning over leaves and pieces of decaying wood or by boring 
holes in soft mud. He also saw them chasing frogs, and once saw a 
raven harass a domestic cat, which was carrying a mouse, into dropping 
the mouse and then distract the cat while another raven made off with 
the mouse. 

Mallory (1977) observed a raven in Ontario flying from a perch 
and breaking the tunnels of voles ( Microtus pennsylvanicus ) to expose 
and flush the mammals. 

Marquiss et al . (1978) witnessed a pair of ravens in Britain 
robbing voles from short-eared owls ( Asio flammeus ). After observing 
concentrations of foraging ravens along the Trans-Canada Highway, 
Conner and Adkisson (1976) suggested the ravens were feeding on 
migrant birds killed by passing vehicles. 



VOCALIZATIONS 

The common raven is believed to have a repertoire of vocali- 
zations as extensive as any bird species, although this repertoire is 
nearly equalled by that of the crow (Brown, 1974; Jollie, 1976). 
Brown (1974) discovered that ravens in Alaska have a range of vocal 



19 



frequencies that extends from 300 cycles per second (c/s) to 2,300 c/s 
for fundamental frequencies, and harmonics extended above 8,000 c/s. 
Raven calls carry considerable distances and are thus well suited for 
communicating in dense habitat (Ross, 1925; Zirrer, 1945; Brown, 
1974). 

Determining the raven's exact repertoire is complicated by 
individual variability and plasticity of behavior (Bowles and Decker, 
1930). Brown (1974) was able to identify over 30 distinct call 
categories on the basis of audible and audiospectrographic charac- 
teristics. He was able to detect up to 10 sub-syllables in some of 
the calls, although most contained only one. "Kaww" and "Koww" calls 
were the most frequent vocalizations and were extremely variable 
within the population. Harlow (1922) described male ravens as having 
a much deeper and stronger call than females. The call of young 
ravens is easily distinguishable up to the age of 6 months (Harlow, 
1922). 



SOCIAL BEHAVIOR 

Corvids, including ravens, are believed to have the most complex 
playing behavior known among birds (Ficken, 1977). Thompson (1964) 
observed ravens carrying pieces of twigs and heather and dropping and 
catching them in mid-air, and Elliot (1977) observed ravens hanging 
upside down by their beaks and feet from a tree branch. Dorn (1972) 
witnessed ravens tearing off small pieces of paper with their bills 
and saw two ravens tugging on a piece of paper until it tore. Gwinner 
(1966) considered play behavior among ravens to be contagious with 
birds showing a great deal of individual variation and invention in 
developing complex behavioral sequences. 

Dorn (1972) observed ravens in Wyoming displacing other ravens 
perched on a gravel pile only to be displaced themselves by other 
ravens. The ravens displayed similar behavior as they sat on a fence 
rail. One would sidle along the fence and attempt to dislodge 
another. The displaced birds would fly and land and then displace 
others from the rail. 

Another commonly observed form of social behavior is aerial 
soaring (Rubey , 1933; Hutson, 1945; Zirrer, 1945; Hewson, 1949; 
Hurrell, 1951; Lockley, 1953; Hewson, 1957; Davis, 1967; Dorn, 1972; 
Brown, 1974). Flocks of ravens, ranging from several pairs to over 
100 birds, engage in spectacular aerobatic and soaring flights near 
hills or cliffs that provide thermals. 

Hurrell (1951) and Brown (1974) believe that ravens are attracted 
to areas with good thermal characteristics when social flying, and 
Hewson (1957) believed that the stimulus for social flying is the 



20 



sight of other ravens already playing or soaring in a thermal. Davis 
(1967) observed that ravens fly over a mile to join an aerial display. 

There is disagreement over exactly the time of year that social 
flying occurs, its purpose, and whether it consists of mated pairs 
and/or non-breeding birds. It does appear that, depending on the time 
of year, mated pairs, as well as non-breeding birds, do participate in 
social flocking (Jollie, 1976). Coombes (1948) and Brown (1974) be- 
lieve that social flocking is not motivated by food. 

Jollie (1976) considers the raven to be an aggressive bird with a 
relatively greater tolerance distance than other related species, and 
reports that a dominance hierarchy exists during such times as feed- 
ing. Dorn (1972), however, was unable to discern any hierarchy within 
a flock of birds at a Wyoming garbage dump, but did observe that some 
sort of flock integrity was maintained through calling. This was also 
observed by Brown (1974), who felt that a social hierarchy did exist 
at an Alaskan dump. He believed that this was maintained by threaten- 
ing and submissive postures. Adults were never seen fighting, but 
juveniles frequently fought. 



ROOSTING 

Communal roosting is a common feature of corvid behavior. It is 
generally believed that winter roosts are comprised of breeding and 
non-breeding birds, but that during the nesting season, only non- 
breeding birds occur in roosting and feeding flocks. Coombes (1948) 
and Ratcliffe (1962) believe that mated pairs roost alone on their 
breeding territories during the winter. 

Cushing (1941) observed up to 200 ravens roosting in a bushy 
canyon along the coast of Marin County, California. This roost had 
apparently been used for at least 9 years. Some birds that fre- 
quented the roost traveled over 40 miles each day between the roosting 
and foraging sites and back. 

In the Baraga Plains, Michigan, Mahringer (1970) observed a 
communal roost with a maximum of 60 birds. This roost site was used 
from June until mid-August when logging operations began. 

Lucid and Conner (1974) reported a winter communal roost in 
Virginia of over 100 birds. The roost was in a clump of hemlocks 
( Tsuga canadensis ) that the researchers located by observing the 
aerial soaring and aerobatics of the ravens over the roost site before 
settling down for the night. This roost site had apparently been used 
for several years. Temple (1974) described a roost of about 10 ravens 
that had been active for several years in abandoned buildings in 
Alaska. 



21 



Perhaps the largest communal roost of ravens in North America is 
located within dense growths of bulbush ( Scirpus acutus ) at the 
Malheur National Wildlife Refuge in Oregon (Stiehl, 1978). Ravens 
roost directly on the frozen substrate or on slightly elevated JS. 
acutus stems. On January 4, 1977, 836 ravens were counted at the 
roost site. Banded birds that used this winter roost were seen as far 
as 298 miles away during other seasons indicating that the roost 
attracted ravens from considerable distances. During 1976 and 1977, 
the roost was active from mid-October until mid-March, with a maximum 
number of ravens observed in early January. 

Several pre-roost areas were located within a mile of the roost 
area. Stiehl (1978) observed that ravens might or might not include 
stops at pre-roost sites. He observed that birds that arrived early 
did stop at the pre-roost site, while late arrivals flew directly to 
the roost site. Flights from the pre-roost area to the roost site 
were low and direct. When over the roost site, the birds folded their 
wings and tumbled into the S^. acutus . 

Morning activity in the roost began before sunrise. Shortly 
after vocalizations began (croaks and buzzes), the ravens would start 
leaving the roost. Initial flights were short, between 1,200 and 
3,000 feet, and in small groups. From these staging areas, long, 
almost continuous flights would take the ravens to grain fields and 
carrion sites up to 28 miles away (Stiehl, 1978). 



22 



HABITAT REQUIREMENTS 



FACTORS INVOLVED IN NEST SITE SELECTION 

Much of the raven's success in fledging young is dependent on the 
nest site. Jollie (1976) described a pair that nested at one cliff 
for 14 years, but were only successful in fledging young once because 
the nesting cliff was in an area inhabited by people. Nest site 
selection, as well as habitat preference, is largely learned, which 
could explain why some ravens nest in trees in areas containing cliff 
sites (Jollie, 1976). In Virginia, Harlow (1922) observed that raven 
pairs always use the same nesting substrate regardless of whether that 
substrate was the most available. 

In England, Ratcliffe (1962) noted that physiographical and 
geological diversity affected ravens' breeding density. The smallest 
nesting cliff used depended on what was available and was therefore 
related to topography (Ratcliffe, 1962; Stiehl, 1978). Cliffs from 
200 to 500 feet high were most favored. The largest cliffs were used 
the most regularly by nesting ravens since they provided the most 
security. 

Ratcliffe (1962) noted that small and unsuitable nesting cliffs 
are used only if they are far enough from main roads and habitations. 
Of 34 raven nesting cliffs that were less than 50 feet high, only 6 
were less than a mile from human habitation. Conversely, of 87 raven 
nesting cliffs that were within a half mile of human habitation, only 
15 were less than 100 feet high. 

In Virginia, however, Hooper (1975) found that nearly as many 
nesting cliffs that were less than 45 feet high were found less than a 
half mile from human habitation as were found in more secluded loca- 
tions, and that an equal number of taller cliffs were found in both 
locations. On the average, more successful nesting attempts occurred 
closer to roads and dwellings than did unsuccessful ones, and success- 
ful nesting attempts less than a quarter mile from a road averaged 
more fledgings than did attempts farther away. This may have been due 
to food availability, since more suitable prey could be found in the 
valleys and near railroads, houses, farms, and most roads. 

Harlow (1922) seldom found a nest in Virginia less than 50 feet 
high and found some on cliffs up to 200 feet high, but noted that the 
height of the nesting cliff was of secondary importance. Hooper 
(1977), also in Virginia, observed nesting cliffs between 15 and 114 
feet, averaging 59 feet high. Nests that were higher on cliffs were 
no more successful than the lower nests. Conner et al. (1976) 
observed that the typical nest cliff height was between 30 and 60 



23 



feet, and Murray (1949) found nesting cliffs in Virginia from 75 to 
100 feet high, with nests placed from 20 to 60 feet from the base of 
the cliff. 

In Idaho, Kochert et al. (1977) noted that ravens seemed to nest 
on smaller cliffs than did other raptor species, with nests found 
between 17 feet above the cliff base and 12 feet below the cliff top. 
The total relief and lateral extent of a nesting cliff were just as 
important as the sheer height of the cliff. 

McBee (1937) noted that nesting cliffs in Washington were never 
high, averaging between 40 and 50 feet. Decker (1930) found that six 
nesting sites were an average of 22 feet above the cliff base, with a 
range of 12 to 40 feet, and 11 feet below the cliff top, with a range 
of 10 to 12 feet. 

Ratcliffe (1962) noted that ravens in England did not nest above 
2,700 feet elevation, but preferred nesting between 1,250 to 1,500 
feet because of the severe climate at higher elevations. Although 
ravens are capable of nesting in severe weather, the prolonged snow 
cover and low temperatures above 2,500 feet elevation were believed to 
restrict nesting. On the other hand, raven nests were seldom found 
below 500 feet above sea level (Ratcliffe, 1962), mainly due to an 
absence of suitable nesting cliffs and high human disturbance. 

Hooper (1975) noted that ravens in Virginia nested between 1,005 
and 3,390 feet, although this was probably due to cliff availability. 
Eighteen nests were found between 1,005 and 1,737 feet, 12 between 
1,740 and 2,637 feet, and 11 between 2,640 and 3,390 feet. The number 
of nests fledging at least one young was no different above and below 
1,740 feet, but significantly more young were fledged per successful 
nest attempt below 1,740 feet than at higher elevations. 

Smith and Murphy (1973) found that the average elevation of nest- 
ing ravens in their Utah desert study area was 5,950 feet, with a 
range of 5,590 to 6,320 feet. White and Cade (1971) believed that the 
altitudinal limit for nesting ravens in Alaska was 3,500 to 4,000 feet 
and that many magnificent cliffs were therefore unsuitable for 
nesting. 

In England, Ratcliffe (1962) noted that most nesting cliffs faced 
between north and east, although actual nest site exposure deviated by 
as much as 90 degrees. He believed that nest exposure did not influ- 
ence the choice of nesting cliff or site. Nesting cliffs in Virginia 
faced northeast to southwest, with 18 nest sites facing south to west 
and 10 facing north to east. Ten other nest sites were on the sides 
of ridges (Hooper, 1975). In Utah, Smith and Murphy (1973) determined 
that 57.1 percent of the nest sites faced west, 28.6 percent faced 
north, and 14.3 percent faced south. They also observed that all the 
raven nests had overhangs preventing direct exposure. 



24 



Protective overhangs are apparently common to most raven cliff 
nests (Harlow, 1922; Wolfe, 1929; Jones, 1935; Murray, 1949; 
Ratcliffe, 1962; White and Cade; 1971; Smith and Murphy, 1973; Conner 
et al. , 1976). Harlow (1922) observed that since egg-laying often 
begins in February when winter storms are common, an overhang assures 
protection. Ratcliffe (1962) also noted that overhung nests are 
protected from wind, falling stones and ice. In Virginia, Hooper 
(1975) noted that overhanging ledges ranged from .8 to 236 inches. 



NEST SITES 

Ratcliffe (1962) observed that in England ravens usually use 
several nest sites and several nesting cliffs. Ten different nest 
sites was the maximum found on a single cliff. In some cases, indivi- 
dual pairs had up to six alternate nesting cliffs, although two or 
three was the norm. Usually, one nesting cliff was preferred over the 
others, although the others were occasionally occupied (Fig. 2). Ratcliffe 
(1962) observed that alternate nesting cliffs were seldom more than 3 
miles apart. Hooper et al. (1975) noted that ravens in Virginia used 
alternate nesting sites varying from 75 yards to 2 miles apart. 

Jollie (1976) believed that cliff sites are better than non-cliff 
sites since a large nest can more easily be built on a ledge than in a 
tree. Thus, trees are used only when absolutely necessary. In Penn- 
sylvania, Harlow (1922) found that cliff nests outnumbered tree nests 
eight to one. When trees were used, they usually were the tallest 
available, with good cover at the tops. Dorn (1972) located 32 nests 
in cottonwood or aspen trees in Wyoming that were between 15 and 100 
feet high. Fig. 2A depicts a raven nest in a Yucca in New Mexico. 

Until 1945, tree nesting was unusual in the Scottish border 
counties, but after suitable cliffs were occupied, ravens began nest- 
ing in trees (Ratcliffe, 1962). Tyrrell (1945) noted that where 
cliffs were not available, ravens often constructed nests in tall 
pines. Although Tyrrell observed the same tree nests being used year 
after year, Harlow (1922) reported that tree nests were never used two 
years in a row. Hooper (1975) located only three tree nests in a 322- 
mile area. The nests belonged to the same pair that attempted to 
build a nest on a cliff but failed because the ledge was too steep to 
hold the nest. 

Ravens are remarkably adept at using man-made structures for 
nesting sites. Dorn (1972) observed a nest in a hay shed, and 
Truesdale (1908), Bowles and Decker (1930), and Congdon (1948) 
observed ravens in California and Washington nesting in abandoned 
barns and houses. Bowles and Decker (1930) also saw ravens using 
railroad trestles, telephone poles, and windmills as nesting sites. 



25 





Figure 2. Natural nesting sites of common ravens on 
cliffs or rocky outcroppings. 



26 




Figure 2A. 
Mexico . 



Nest of common raven in Yucca in New 



27 



Thompson (1919) reported a pair of ravens nesting in a 75-foot high 
transmission tower that carried a 130,000 volt transmission line. Of 
65 nests at the Birds of Prey Natural Area in Idaho, Kochert et al. 
(1977) observed that 61 were on cliffs, 1 was in a tree, 1 was on an 
artificial platform, and 2 were on powerline structures. The authors 
of this Technical Note have also found ravens nesting under bridges, 
on wooden and steel power poles, in windmill structures, and on water 
pumping platforms. Figs. 3 and 3A show some common artificial nest sites, 



TERRITORY SIZE 

There is some confusion as to whether or not ravens are truly a 
territorial species. In Oregon, Stewart Janes (1980, pers. comm.) 
observed that ravens did not appear to defend territories. Extensive 
home range overlap occurred, yet the even spacing suggests that some 
form of territoriality existed. Smith and Murphy (1973) detected very 
little intraspecif ic home range overlap in Utah, even though the 
ravens were known to have large home ranges, and considerable overlap 
did occur with other raptor species. Dorn (1972) observed intra- 
specific territorial defense in which the defenders were vocal and the 
intruders were silent. Yet she also observed at times that intra- 
specif ic nest defense was weak, with a breeding pair chasing an 
intruder only a short distance. When a flock of conspecifics invaded 
a nesting territory, the breeding pair would perch near their nest and 
remain silent. Craighead and Craighead (1969) noted that although the 
nesting territory was defended against other ravens and hawks, the 
entire range was not. 

Ratcliffe (1962) felt that ravens in England were not terri- 
torial in the sense that they aggressively defended an area. Yet he 
noticed that they were evenly spaced throughout an area with most 
pairs keeping their nesting sites a certain distance apart. Nest 
locations were markedly nonrandom, indicating that some factor was 
operating to keep nesting pairs spaced. Ratcliffe (1962) speculated 
that something other than aggression, such as aerial displays or 
psychological inhibitions, may have been the actual mechanism, but 
that the effect on distribution was nevertheless indistinguishable 
from that produced by territorialism. 

In four distinct areas in England, varying in size from 170 to 
441 square miles, Ratcliffe (1962) determined that the average 
territory size ranged from 6.6 to 17.6 square miles. In these same 
four areas, the average minimum distance between nests was 1.7 miles 
in three of the areas and 2.9 miles in the fourth. The Anglesey sea 
cliffs on the British Isles supported four nesting pairs on a linear 
distance of 2 miles. 



28 





Figure 3. Common raven nests on artificial or man-made 
structures. Ravens will nest in a wide variety of artificial 
sites from bridges to windmills. 



29 







-*$* 



~ - - i 

I 

■ • f 



•i 





Figure 3A. A raven nest in a grain elevator in 
Washington state. 



30 



Hooper et al. (1975) observed a density of one pair per 19 square 
miles in a 322 square mile area in Virginia. The mean distance to the 
nearest active nest was 3.0 miles in 1973 and 3.2 miles in 1974. In 
Pennsylvania, Harlow (1922) observed that the nearest distance between 
any two pairs of nesting ravens was six miles, and in Wisconsin, 
Zirrer (1945) observed that raven territories averaged 10 miles in 
diameter. Dorn (1972) noted that ravens in Wyoming nested at least a 
half mile apart, although there were two pairs that were separated by 
a hill with their nests only a quarter mile apart. Also in Wyoming, 
Craighead and Craighead (1969) found the home ranges of three pairs of 
ravens to be 3.62 square miles. 

In Utah, Smith and Murphy (1973) determined that the average 
distance between nests was 1.08 miles, ranging from 0.55 to 1.84 
miles. The average home range was 2.53 square miles. 

The Birds of Prey Natural Area in Idaho has one of the most dense 
raptor populations in North America. According to Kochert et al. 
(1975), 49 pairs of ravens nested there in a 52 square mile area. In 
1976, they found that the average minimum distance between raven nests 
was 1.56 miles and attributed more than 50 percent of the variation in 
raven pair numbers to cliff availability. Numbers were higher in 
areas with more nesting cliffs. 

In Oregon, Stiehl (1978) observed that raven nest density in 
Harney Basin averaged one pair per 13.6 square miles in 1976, and one 
pair per 15.7 square miles in 1977. Elsewhere in Oregon, Stewart 
Janes (1980, pers. comm. ) determined that home ranges were between 3 
and 6 square miles. 

R. Wayne Campbell (1980, pers. comm.) observed that two pairs of 
ravens nested only 300 yards apart for over 6 years at the Lt. 
Governor's house in Victoria, British Colombia. In Alaska, White and 
Cade (1971) reported that nesting ravens averaged 21.1 miles apart, 
with a range of 3.5 to 102 miles. 



31 



INTERSPECIFIC RELATIONSHIPS 



The relationship between ravens and a wide variety of other 
species has been well documented by numerous observers. Ficken (1977) 
states that ravens may "play games" with different animals, including 
man, while Jollie (1976) cautions that much of what has been called 
"play" involves an aggressive outflow of spirit. White et al. (1975) 
stated that ravens can compete with raptors and can unfavorably modify 
to some degree their habitat. They noted that ravens in large numbers 
may be detrimental competitors, often using similar food sources. 

Perhaps the best documented relationship between ravens and other 
species is that which exists with falcons. It is generally considered 
a commensal relationship (White and Cade, 1971). Bowles and Decker 
(1930) and Decker and Bowles (1930) were the first to comment exten- 
sively on the relationship between prairie falcons ( Falco mexicanus ) 
and ravens. In Washington, Parker (1973) observed ravens nesting 
within 20 feet of a pair of prairie falcons that were nesting in an 
abandoned raven nest. Since the nesting requirements of the two 
species are almost identical, prairie falcons often use old raven 
nests. Decker (1931) mentioned finding six raven nests in Washington 
being used by prairie falcons. Additionally, he stated that "without 
ravens to build nests where suitable cavities are missing, the prairie 
falcon would not be there." Bowles and Decker (1930) and Porter and 
White (1973) have observed a similar phenomenon. 

Howard et al. (1978) reported that in an undisturbed habitat in 
Idaho, prairie falcons represented almost 30 percent of the raptor 
population and ravens 14 percent, but in areas where farming was 
intensive or where there was an abundance of cheatgrass ( Bromus 
tectorum ) or crested wheatgrass ( Agropyron cristatum ), the number of 
ravens equalled or surpassed the number of prairie falcons. 

Although ravens usually initiate nesting earlier than do prairie 
falcons and are, in many areas, living within their territories, 
prairie falcons are still able to usurp raven nests (Decker and 
Bowles, 1930). 

Harlow (1922) reported a raven nest within 40 feet of an active 
peregrine falcon (Falco peregrinus ) eyrie, while Jones (1935) observed 
ravens and peregrines nesting only a few hundred feet apart on a cliff 
in Virginia. The peregrines were nesting in an inactive raven nest. 
Harlow (1922), Jones (1935), Craighead and Craighead (1939), and 
Murray (1949) felt that peregrine falcons were dominant over ravens, 
although Cade (1971) observed ravens nesting 50 yards from a pair of 
peregrines in the Alaskan Arctic where the ravens were usually the 
aggressors in almost continuous territorial battles. Ratcliffe (1962) 
was not aware of any case in which nesting ravens had displaced 
peregrines, although he had observed peregrines and ravens nesting 



32 



only 10 yards apart. Porter and White (1973) observed no evidence of 
a beneficial relationship between peregrine falcons and other cliff 
nesting species in Utah that was similar to the relationship between 
the prairie falcon and raven. 

The gyrfalcon and raven are both early breeders and have almost 
identical nesting requirements in the Arctic (Cade, 1960; White and 
Cade, 1971). White and Cade (1971) observed the two species nesting 
only 60 yards apart, while Jenkins (1978) witnessed ravens and gyr- 
falcons in Greenland successfully nesting only 150 feet apart. Cade 
(1960) felt that gyrfalcons sometimes expelled ravens from suitable 
nesting cliffs when there was limited space, but pointed out that 
ravens have free access to such cliffs during years when gyrfalcons do 
not nest because of food shortages. 

White and Cade (1971) described a possible commensal relationship 
between ravens' and gyrfalcons in which ravens favorably modified the 
gyrfalcons 1 nesting environment by their stick nests. At the same 
time, ravens augmented their diets by scavenging the remains of gyr- 
falcon prey. 

In Utah, Smith and Murphy (1973) found that golden eagle ( Aquila 
chrysaetos ) nesting sites overlapped considerably with those of the 
common raven. Marquiss et al. (1978) reported that four nesting 
pairs of ravens were displaced by golden eagles. Rubey (1973), Smith 
and Murphy (1973), and Dunstan (1975) observed that interactions 
between the two species were initiated by the ravens. Dunstan (1973) 
speculated that ravens and golden eagles might mutually benefit from 
the overlap if one located carrion that could be used by both. When 
two golden eagles flew over a group of 40 ravens feeding on carrion in 
Washington, the ravens took flight with much calling until the eagles 
passed on. 

Jollie (1976) observed that ravens seldom attack crows, which can 
outclimb and outmaneuver the larger bird. As individuals, the ravens 
dominate the crows, although crows can dominate when in large enough 
numbers to harass the raven (Zirrer, 1945; Jollie, 1976). 

Zirrer (1945) and Williamson and Rausch (1956) reported goshawks 
(Accipiter gentilis ) chasing ravens, and Zirrer observed goshawks 
excluding ravens from a summer feeding area. He also observed a 
single eastern kingbird (Tyrannus tyrannus ) driving off a group of six 
ravens from a pond where they had been feeding and near where the 
kingbird had a nest. 

Bowles and Decker (1931) observed male red-winged blackbirds 
( Agelaius phoeniceus ) driving three ravens from a nesting area in 
Washington. In a barn in California, Truesdale (1908) found an active 
raven nest with five eggs in which a pair of barn owls ( Tyto alba ) 



33 



were also nesting. Smith and Murphy (1973) observed ravens attacking 
golden eagles, red-tailed hawks ( Buteo ja maicensis ) , prairie falcons, 
and American kestrels ( Falco sparverius ). Craighead and Craighead 
(1939) observed a raven climbing above and attacking a broad-winged 
hawk ( Buteo platypterus ). In Alaska, Cade (1961) observed a pair of 
ravens nesting within 100 yards of a pair of rough-legged hawks ( Buteo 
lagopus ), and reported almost continual territorial battles between 
those two pairs and an adjacent nesting pair of peregrine falcons, 
with the ravens initiating most of the fighting. 



Summary of the Ecological Importance of Ravens 

1. Ravens provide nesting platforms for many species of raptors. 

2. They feed on carrion and help in the breakdown of organic 
material. 

3. They serve as "aerial advertisers" of carrion to other 
scavenging species. 

4. Ravens help "dampen" cyclic fluctuations of certain rodents. 

5. They are involved in the lives of a great many other species of 
animals and birds, causing harassment, death, or stress in many, 
while having beneficial influences on many others. 

6. Their high intelligence permits them to perform many unusual and 
unexpected acts in Nature. They are highly social at certain times 
of the year. 



34 



LIMITING FACTORS 



Jollie (1976) considered the common raven to be one of the most 
generalized species known as far as the variety of habitats it occu- 
pies. It can be found from the far north, where it not only nests but 
also winter, through the boreal and conifer forests of North America, 
across the American Desert, north to Labrador, down the Applachian 
Mountains to Georgia and throughout Mexico. 

The common raven is a long-lived species, has a relatively large 
clutch size, and shows remarkable population stability and an attach- 
ment to historic nesting sites. Nesting success ranges from seldom 
producing young to fledging three to four young per year. A substan- 
tial portion of the population is composed of non-breeding birds which 
act as a buffer to the overall population and which can attempt to 
breed in peripheral habitat and colonize new areas (Jollie, 1976). 



NESTING SITES 

The natural supply of nesting sites in the raven's diverse 
habitats does not appear to limit its population (Jollie, 1976). 
Because of its adapatabilty in using a wide assortment of artificial 
structures, the raven is virtually assured of finding a nesting site. 

In England, Ratcliffe (1962) reported that suitable nesting sites 
were often not used, indicating that some other factor was limiting 
the population. Hooper et al. (1975) noted that since less than 
one-third of the potential nest cliffs were used in their Virginia 
study area, the number and distribution of cliffs did not appear to be 
a limiting factor. White and Cade (1971) considered the nesting cliff 
in Alaska to be the most important physical feature around which the 
raven centers its life. The distribution of nesting ravens was 
closely associated with the occurrence of these nesting sites, yet 
there were suitable cliffs and bluffs available which were not used. 
White and Cade (1971) speculated that through some sort of social 
convention or tradition, ravens perhaps restricted nesting to certain 
cliffs. 



FOOD 

The common raven has also adapted to widely scattered and vari- 
able food sources (Jollie, 1976). Because they live in such a wide 
variety of habitats and are omnivorous, the raven population is not 
usually limited by food. Although there were seasonal variations in 
food supplies in Ratcliffe 1 s (1962) study area in England, the 



35 



total food supply was available in excess and remained constant from 
year to year. Therefore, in this study area, the food supply did not 
appear to directly limit the population. 

Marquiss et al. (1978) found that in southern Scotland and 
northern England, the raven's food supply increased with deteriora- 
tion of the land productivity, since there was higher domestic sheep 
mortality in areas of overlying acidic rock. Thus, they concluded 
that raven dispersion and density were based mainly on food supply. 
They also found that ravens bred less often and produced later, 
smaller broods in areas that had been heavily afforested. By 1974 and 
1975, only 55 percent of the formerly occupied nesting areas were 
still occupied, and breeding pairs had declined by 44 percent. This 
appears to be the best available evidence of the importance of food, 
substantiating the belief that a lack of food may limit raven popula- 
tions and/or density. 

In Virginia, Hooper et al. (1975) believed that food supply could 
have affected the raven population by influencing the survival of 
asynchronously hatched nestlings. Significantly more young were 
fledged in successful nesting attempts at lower elevations. This may 
have been the result of a greater food supply existing in the valleys 
where railroads, houses, farms, and most roads were located (Hooper, 
1977). Ravens that nested at higher elevations may have had to spend 
more time foraging away from the nest, which could have affected 
nestling survival. 

In Michigan, Mahringer (1970) noted a sharp decline in the popu- 
lation density of ravens during the summer of 1969 and attributed it 
to a decline in food availability and disturbance of raven feeding and 
roosting activities. 

Dorn (1972) in Wyoming and Stiehl (1978) in Oregon indicated that 
winter appeared to be a time of food stress, at which time ravens 
relied heavily on garbage, carrion and cultivated grain wastes. Since 
winter may be a critical time of food stress for ravens, perhaps the 
communal roosting habit would be especially advantageous. Ward and 
Zahavi (1973) discussed how communal roosting and colonial nesting 
increased efficiency in locating an unevenly distributed food supply. 



HUMAN DISTURBANCE 

Ratcliffe (1962) observed that while human disturbance, such as 
shooting, rock climbing, rock quarrying, and egg collecting from raven 
nests did cause temporary reduction in the number of nesting ravens, 
it did not appear to have had any permanent effect on breeding den- 
sity. In Scotland and England, Marquiss et al. (1978) observed that 
raven nesting sites were abandoned where rock climbing took place, and 
another nesting cliff was deserted following the construction of a 



36 



small reservoir and pumping house below the nest. In addition, 
several clutches were taken by egg collectors and two cases of 
poisoning were reported. 

Hooper (1977) noted that in Virginia, the shooting of ravens was 
of only minor importance, although several birds that dug for grubs on 
a golf green and another that robbed golf balls were shot. The 
ability of ravens to adjust to human disturbance varied greatly. The 
nests most subject to human disturbance fledged young in two succes- 
sive years, then were not used for two succeeding years. Harlow 
(1922) believed that neither egg collecting nor shooting were serious 
factors in the decline of raven populations in Pennsylvania, but that 
roads or houses built too close to nesting cliffs did cause nest 
abandonment. Murray (1949) visited a nesting site for 11 years 
without causing the ravens to abandon the nest. A nesting cliff would 
be used again and again, even if the birds were often disturbed by 
humans (Tufts, 1916). Both Tyrrell (1945) and Sprunt (1956) believed 
that human persecution was the primary factor in the decline of ravens 
in the eastern United States. 

In Idaho, Kochert et al. (1977) noted that fewer ravens fledged 
from nests that were first visited during incubation (1.7 young per 
attempt) than were visited after the young were at least one to two 
days old (between 1.6 and 5.0 young per attempt). Nests visited for 
food habit data at 4-day intervals had higher fledging rates than did 
control nests (Kochert et al. , 1976). This was considered to be more 
a result of careful research techniques than an inference that egg and 
nestling survival were independent of human activity. 



LOGGING 

Harlow (1922) remarked that lumbering near raven nest sites in 
Pennsylvania, as well as the encroachment of civilization, were the 
main reasons for their decline. Mahringer (1970) noted that the 
declining attendance in a communal roost in Michigan coincided with 
logging operations in that area. 



CHEMICAL CONTAMINATION 

Ratcllffe (1970) failed to detect any significant eggshell thin- 
ning of 205 raven eggs from various parts of Britain following the 
introduction of DDT. Marquiss et al. (1978) likewise failed to detect 
any eggshell thinning. In addition, organochlorine levels were very 
small and, compared with birds of prey, would have had no influence on 
raven breeding performance or population. 



37 



Kochert et al. (1975) tested the total mercury level in one Idaho 
raven egg and found it to be below the level that would cause death or 
physiological malfunctions in raptors. 






38 



ECONOMIC CONSIDERATIONS 



Ross (1925) reported that ravens on Catalina Island, California, 
picked out the eyes of new-born lambs, but were unable to hurt young 
goats. In Washington, McBee (1937) stated that although ravens were 
reported to have killed lambs, he had never heard sheepmen complain of 
losing sheep. Larsen and Dietrich (1970) reported that in Oregon, 
ravens killed newborn lambs by driving their beaks into an eye socket 
before the lamb could get to its feet. From cursory collection of 
dead lambs in their study area, 72 were believed to have been killed 
by ravens. 

Bowles and Decker (1930) considered ravens near breeding water- 
fowl to be highly injurious because of the number of eggs and young 
they destroyed. In Wyoming, Dorn (1972) determined that ravens did 
not have a detrimental effect on any animal population in the study 
area, but Craighead and Craighead (1969) and Dimmick (1949) believed 
ravens were important predators on waterfowl eggs and young. Dorn 
(1972) speculated that individual ravens may have learned that human 
activity causes waterfowl to flush from their nest, and this provides 
an opportunity for predation on either the eggs or young of these 
nests. 

At Malheur Lake, Oregon, Ferguson et al. (1976) considered the 
raven to be the principal cause of nesting failure among greater sandhill 
cranes ( Grus canadensis ), since windmills and other artificial nesting 
sites in the area have enabled ravens to nest closer to the lake. 
Stiehl (1978), in his intensive study of raven food habits in the 
Harney Basin, Oregon, determined that ravens nesting in wetland areas 
near high waterfowl concentrations were more likely to be involved in 
nest depredations, but concluded that this was not a priori evidence 
of waterfowl predation. He noted that individual pairs were respon- 
sible for the majority of the nest depredations. Stiehl (1978) noted 
that much of the waterfowl predation might have been by non-nesting 
birds that frequent the waterfowl areas in the summer. 

Dorn (1972) and Stiehl (1978) believed that closing dump sites 
would probably decrease the number of ravens frequenting an area. 
Stiehl (1978) also indicated that live trapping of ravens in the 
winter months might be an effective way to decrease their numbers. 
Live decoy ravens and large volumes of carrion are needed to success- 
fully trap birds. Stiehl (1978) recommended that trapped ravens 
should be relocated a minimum of 124 miles from the trap site. He 
believed that the direct shooting of birds was impractical and would 
have a minimal affect on population reduction. 

Larson and Dietrich (1970) suggested that baiting with cubed meat 
treated with DRC-1339 would be a successful technique for controlling 
large numbers of ravens. Injections of DRC-1339 in the eyes of 



39 



carcasses was effective where only a few ravens were involved. Stiehl 
(1978) suggested that .0338 U.S. fluid ounce of water containing .0007 
ounce DRC-1339 injected in eggs would be effective in selectively 
reducing the population. Stiehl (1978) recommended that any manage- 
ment plan for reducing the number of ravens should include a compari- 
son of pre-management predation rates with post-management predation 
rates, as well as a comparison of the management area with a control 
(non-management) area. 

Another viable alternative to waterfowl predation management 
would be to improve waterfowl nesting habitat. Stiehl (1978) dis- 
cussed the implications of waterfowl renesting and the importance of 
nesting cover to waterfowl production and suggested that habitat 
improvement was more beneficial and effective than raven control 
operations. 



40 



SPECIES AND HABITAT MANAGEMENT RECOMMENDATIONS 



1. Kochert et al. (1976) found that nest visits, if properly con- 
ducted, did not affect the number of ravens fledged from nests. 
Nevertheless, ravens are susceptible to disturbance near nest 
sites. Rock climbing activities, for example, will cause ravens 
to abandon a nesting cliff. Logging operations and general human 
disturbance may cause ravens to abandon communal roost areas and 
feeding sites. 

2. Common ravens are easy targets for shooters. Many people are not 
aware that crows, magpies ( Pica pica ), and ravens are fully pro- 
tected under the Migratory Bird Treaty Act. Public education is 
extremely important to make people aware of the uniqueness and 
ecological importance of the common raven. 

3. Any proposed or current developments on Bureau of Land Management 
administered lands, or developments on other private or public 
lands, should be studied for their possible effect on ravens. 
Nesting sites, communal roosts, and feeding concentration areas 
should be identified prior to any development, and the impact on 
ravens should be assessed. 

4. Further studies are needed to determine the food requirements of 
common ravens and their economic impact on other animal popula- 
tions. Stiehl (1978) determined that most waterfowl depredation 
at Malheur National Wildlife Refuge was the result of non-breeding 
birds that summer near waterfowl production areas and was not 
necessarily caused by nesting birds. This information is criti- 
cally important in any management plan. 

5. Nesting sites, communal roosts, and feeding areas should be 
located and mapped on BLM-administered lands. Baseline informa- 
tion is critically important before management decisions can be 
made. These areas should not be advertised to the general public, 
since many people are unaware that ravens are protected by law and 
that visiting nests and removing young is illegal. People are 
often fascinated by the possibility of obtaining a young raven as 
a pet. Not only is this illegal, it is also difficult to raise 
ravens in captivity. Well-intentioned people who simply want to 
see a raven nest are often unaware of the implications of causing 
premature fledging or causing parents to miss a feeding. Hooper 
(1977) recommended that human activity be curtailed within the 
vicinity of nesting sites, although the actual distance to 
restrict activity would depend on the terrain and type of acti- 
vity. In general, he recommended that pedestrians should not be 
permitted within about 650 feet of a nest if they are visible to 
the birds from the nesting sites, or within about 300 feet if they 
are hidden from view. He suggested that vehicular traffic could 
be allowed as close as 320 feet to a nest, but that parking 



41 



areas should be kept at least 600 feet from the nest. Road con- 
struction within 600 feet of a nest could cause nest desertion. 
Hooper (1977) suggested that rock climbing on nesting cliffs be 
restricted from January 15 until the nestlings fledge in April or 
May. 

Disturbing ravens at communal roost areas is equally harmful. In 
most cases, once ravens have been flushed from a roost site, it 
may take considerable time and energy to resettle for the night. 
This also applies to winter feeding areas. The energetics of 
ravens have not been studied intensively in the field, yet it is 
know that ravens experience food stress during winter months. 

6. Dorn (1972) and Stiehl (1978) suggested closing artificial food 
sites, such as dumps and landfills, to promote a more natural 
situation and to discourage concentrations at these areas. Dorn 
(1972) cautioned that ravens have learned to associate human 
disturbance of waterfowl with unprotected nests and to deliber- 
ately search for the unprotected eggs and young. Any anticipated 
research that might create such a situation should consider the 
impacts of raven pre4ation on the species studied. Stiehl (1978) 
suggested that habitat improvement would be a preferred management 
alternative to the destruction of ravens. Live-trapping and 
removing birds is feasible during the winter, although trapped 
birds should be released at least 124 miles from the trap site. 
Discriminate use of DRC-1339 is feasible in selectively elimina- 
ting individual birds. Stiehl (1978) recommended that .0338 U.S. 
fluid ounce of water containing .0007 ounce DRC-1339 injected in 
eggs would be effective in selectively reducing the population. 



42 



PROTECTIVE MEASURES INSTITUTED 



1. In 1974, the common raven was included in the Migratory Bird 
Treaty Act which gave it complete protection in North America. 

2. In 1971, the Bureau of Land Management established the Snake River 
Birds of Prey Natural Area in Idaho, which exhibits a unique 
concentration of nesting raptors, including ravens. In 1977, 
Kochert et al. (1977) observed 57 nesting pairs of ravens in this 
area and 120 nesting pairs in the total Birds of Prey Study Area. 

3. There are no known attempts of captive breeding or reintroduction 
of common ravens. 



43 



RESEARCH TECHNIQUES 
Call (1978) summarized three important uses for raptor habitat 



data: 



1. To be knowledgeable on important nesting, feeding, wintering, and 
roosting areas in order to give adequate consideration to these 
areas in land management decisions. 

2. To determine and monitor the effects of man's activities on 
nesting or life phases of raptors. 

3. To ascertain general trends in raptor populations and produc- 
tivity, by species, and the probable reasons for those trends. 



Call (1978) suggested that whenever an adult raven is seen during 
the nesting season, there is probably a nest nearby at a suitable 
site, and if the observer watches the bird, it will go to the nest 
site (recognizing, of course, that there are non-breeders in all 
populations). 

Craighead and Craighead (1969) stated that approximately 85 
percent of raptor (including raven) nests were found relatively 
easily, but that the remaining 15 percent required recording and 
mapping of all field sightings. Tree nests were more easily located 
during the winter months when they could be plotted on a map and 
checked again in the spring. The most productive time to locate 
nests, however, was prior to general leafing out and during the early 
period of nest site selection and territorial defense when raptors 
were especially conspicuous (Craighead and Craighead, 1969). Locating 
nests was simplified by the fact that raptors regularly space their 
nests within an area. When one knows approximately how far apart the 
species normally nests, the observer can then determine how many nests 
an area might support. 

Mahringer (1970) studied the population dynamics of ravens in 
Michigan and determined the most productive method of surveying 
numbers and distribution was use of a survey route. Results from the 
survey route were augmented with counts at a communal roost and at a 
feeding area. 

Cannon nets have been used successfully in trapping ravens by 
Dorn (1972) in Wyoming and Mahringer (1970) and Kerttu (1973) in 
Michigan. Mahringer (1970) captured a total of 148 ravens with cannon 
nets. Two cases of mortality resulted from the trapping. 

Neither Mahringer (1970) nor Kerttu (1973) had any success in 
trapping ravens with a drop-in trap similar to that designed by Aldous 
(1938) and Coldwell (1968), but Stiehl (1978) experienced excellent 



44 



success with a drop-in trap (Fig. 4) similar to that of Coldwell 
(1972). Cattle carcasses were used as bait with live raven decoys 
tethered in the vicinity. A total of 99 birds were captured in 44 
trap days during February and March. The trap was inspected at 
two-day intervals and was most successful following periods of snow. 
Schwan and Williams (1978) were successful in capturing ravens in 
Alaska with Havahart single-end traps baited with Purina Dog Chow. 

Mahringer (1970) marked trapped ravens with combinations of two 
or three colored leg bands. The color bands were .75 inch wide by 3 
inches long vinylite strips (Grand Rapids Rubber Products Company, 
Grand Rapids, Michigan) formed by heating and shaping around a wooden 
dowl. Colors used were green, orange, red, white, and yellow. In 
addition, Mahringer (1970) implanted tail feathers with different 
colored goose quills (Herters, Incorporated, Waseca, Minnesota) and 
trimmed them to conform to normal feather shape. 

In Wyoming, Dorn (1972) marked captured ravens with an orange 
patagial tag (Fig. 5), of a double thickness of Safe-T-Flag vinyl 
plastic cemented together and fastened to the upper surface of the 
patagium with a two-piece, aluminum ear button (Fig. 5). A number- 
symbol combination was painted on both sides of each tag with Ram-Cote 
black vinyl upholstery paint. 

In Idaho, Kochert et al. (1977) placed patagial wing markers of 
Herculite 80 (Herculite Protective Fabrics, 1107 Broadway, New York 
10010) on the ravens (Fig. 6). In addition, remiges and/or retrices 
of some ravens were painted with an acrylic base fabric paint for 
specific temporary identification. 

Stiehl (1978) in Oregon marked ravens with wing markers made of 
Saflag (Safety Flag Corp. of America, Pantucket, Rhode Island) and 
Herculite (Vaughn Brothers, Portland, Oregon; Fig. 7). The material 
was cut in a dumbbell shape, about 8x4 inches. White, yellow, blaze 
orange, aurora pink, signal green, light blue and dark blue colors 
were used to give 63 possible color combinations. Markers were 
attached to the wing with the aid of a hand riveter, and .1 x .4 inch 
aluminum rivets together with . 1 inch aluminum backup plates on each 
side. Stiehl (1978) observed no harmful effects of the wing markers 
on ravens and noted that one bird captured 11 months after tagging 
showed no negative effects. 

In his studies of raven vocalizations in Alaska, Brown (1974) 
used a Uher 4000 Report-L recorder and an AKG Model CK9 directional 
microphone to make recordings of the birds. Audiospectrograms were 
produced on a Kay Electric Company Sonograph Model 7029A. 

Hoffman (1920) noted that using raven castings to determine food 
habits was difficult when the birds fed on refuse or carrion because 
there was not enough substance to hold the pellets together for any 



45 




o.6m 



SIDE VIEW 




TOP VIEW 



Figure 4. Diagram of a drop-in trap that has been used successfully 



on 



ravens (from Stiehl 1978). 



46 



22 mm 

I 1 




UI 



7 mm 



5 mm 
3.5 mm 



9.5 





C. 



a. 




d. 




75 mm 



figure 5. Patagial tag assembly: (a) top view of the ear button, (b) side 
view of top and bottom halves of button, (c) two halves put together, 
(d) the button after crimping, and (e) the patagial tag with button in 
place (after Dorn, 1972). 



47 



Raven 




1.0 



1.5 



-¥- 



25 



inches 



Figure 6. General shape and size of wing marker used on common 
ravens in Idaho (Kochert et al . (1977). 



48 



10 cm 





Rivet 
B/U Plate 
Marker 

Wing 



Figure 7. Diagram of a patagial marker for ravens (top) and suggested 
method of attachment of patagial marker to wing of raven (bottom) 
(Stiehl (1978). 



49 



length of time. Kochert et al. (197 7) noted that the high frequency 
of red meat carrion in the raven's diet made it difficult to quantify 
predation rates by conventional means. 




50 



ONGOING RESEARCH PROJECTS 



1. Michael N. Kochert and associates of the Bureau of Land Manage- 
ment, have been studing ravens in the Snake River Birds of Prey 
Natural Area in Idaho since 1974. They have researched the 
raven's complete nesting biology including feeding and movement 
studies. Theirs is perhaps the most exhaustive study ever con- 
ducted on nesting requirements and breeding biology of the common 
raven in North America. 

2. Stewart W. Janes has studied the raptor-raven complex in the 
Oregon desert for six years. He has concentrated on the breeding 
biology of the common raven and its relationship with other 
raptors. 

3. Dr. Norman F. Sloan, Michigan Technological University, has been 
studying the common raven in Michigan since 1968. Two graduate 
students, Mahringer, (1970) Kerttu (1973) have completed Master of 
Science degrees on population dynamics and aging techniques of the 
common raven. Dr. Sloan is currently preparing a manuscript on 
raven nesting requirements in the Upper Peninsula of Michigan. 

4. Dr. Robert G. Hooper, a research biologist for the U.S. Forest 
Service, studied common ravens in Virginia between 1972 and 1974 
and continues to monitor their activities in the southern 
Appalachians. 

5. Dr. Richard B. Stiehl, University of Wisconsin, studied the 
biology of the common raven at Malheur National Wildlife Refuge 
from 1975 to 1977. All aspects of raven biology were included, 
although the study concentrated on food habits of nesting, 
non-breeding, and wintering ravens. 

6. Dr. Malcom Jollie, Northern Illinois University, has conducted 
observational studies on ravens and corvids in general since 1936. 

7. Tony Angell (1977) has conducted general behavioral studies on the 
common raven for the past decade. 

8. Dr. Richard N. Conner, Virginia Polytechnic Institute and State 
University, is studying the biology of the common raven in 
Virginia. 

9. Richard L. Knight, Dr. Richard E. Fitzner, and Tracy L. Fleming 
have been studying the common raven in the Columbia Basin, 
Washington since 1977. Their study involves breeding biology, 
food habits, and winter ecology as they relate to different 
habitat types. 



51 



AUTHORITIES 



1. Michael Kochert 
Boise District 

Bureau of Land Management 
230 Collins Road 
Boise, Idaho 83702 

2. Dr. Richard B. Stiehl 

College of Environmental Sciences 
University of Wisconsin-Green Bay 
Green Bay, Wisconsin 54302 






3. Dr. Norman F. Sloan 
Department of Forestry 
Michigan Technological University 
Houghton, Michigan 49931 

4. Dr. Robert G. Hooper 

Southeastern Forest Experiment Station 

Department of Forestry 

Clemson University 

Clemson, South Carolina 29631 

5. Dr. Richard N. Conner 
Department of Biology 

Virginia Polytechnic Institute and State University 
Blacksburg, Virginia 24061 

6. Dr. Malcom Jollie 
Biological Sciences 
Northern Illinois University 
DeKalb, Illinois 60115 

7. Tony Angel 1 

Office of Enviromental Education 
c/o Shoreline School District 
N.E. 158 and 20th Ave. NE 
Seattle, Washington 98155 



52 



ORGANIZATIONS ACTIVELY INVOLVED WITH 
THE WELFARE OF RAVENS 



1. National Audubon Society , 950 Third Avenue, New York, New York 
10022 

The major objective of the National Audubon Society is to advance 
public understanding of wildlife, its habitat and all natural re- 
sources, and how wise use and intelligent treatment relate to human 
progress. 

2. Raptor Research Foundation , c/o Dr. Donald R. Johnson, Department 
of Biological Sciences, University of Idaho, Moscow, Idaho 83843 

The Raptor Research Foundation stimulates, coordinates, directs, 
and conducts research on the biology and management of birds of prey, 
and promotes a better understanding and appreciation of the value of 
these birds. The Raptor Research Foundation publishes Raptor 
Research , which has articles about the common raven. 

3. Raptor Information Center , The National Wildlife Federation, 1412 
Sixteenth St. NW, Washington, D.C. 20036 

The Raptor Information Center is concerned with the general 
welfare and biology of all raptor species. It has recently published 
two excellent bibliographies, on the owls of the world and the other 
on the bald eagle. 

4. The Nature Conservancy , 1800 North Kent Street, Arlington, 
Virginia 22209 

The Nature Conservancy is a national conservation organization 
that receives its support from the public. Its objective is to 
preserve and protect ecologically and environmentally significant land 
and the diversity of life it supports. 

5. Bureau of Land Management , Washington, D.C. 20240 

The BLM administers approximately 60 percent of the Federal 
lands, most of which are located in the western states. These lands 
are managed under multiple-use principles, including outdoor recre- 
ation, fish and wildlife production, livestock grazing, timber, 
industrial development, watershed protection, and mineral production. 

The BLM is responsible for research and management of the Snake 
River Birds of Prey Natural Area in Idaho. The biologist directly 
working on management plans is Michael N. Kochert, Boise District, 
Bureau of Land Management, 230 Collins Road, Boise, Idaho 83702. 



53 



LITERATURE CITED 



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American Ornithologist's Union. 1957. Check-list of North American 
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Angell, T. 1977. The efficient use of energy: One family's 
strategies. Pac. Search 11:12-14. 

Anonymous. 1967. Report of Huron Mountain Wildlife Foundation, 
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Ayre, R. 1961. Sketco the raven. Macmillan Co. of Can. LTD, 
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Bancroft, G. 1927. Notes on the breeding coastal and insular birds 
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Barrows, W.B. 1912. Michigan bird life. Spec. Bull., Dept. Zool. 
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Bendire, C. 1895. Life histories of North American birds, from the 
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Bent, A. C. 1968. Jays, crows, and titmice. Vols. I & II. Dover 
Pubis., Inc., New York. 

Bowles, J.H. , and F.R. Decker. 1930. The ravens of the state of 
Washington. Condor 32:192-201. 

Bowles, J.H., and F.R. Decker. 1931. Limicolae smearing mud on their 
eggs. Murrelet 12:82. 

Brown, R.N. 1974. Aspects of vocal behavior of the raven ( Corvus 
corax ) in interior Alaska. M.S. thesis, Univ. Alaska, 
Fairbanks. 

Cade, T.J. 1960. Ecology of the peregrine and gyrfalcon populations 
in Alaska. Univ. California Pub. Zool. 63:151-290. 

Call, Mayo W. 1978. Nesting habitats and surveying techniques for 
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Coldwell, C. 1968. Raven banding in Nova Scotia. I.B.B. News 
39:68-69. 



54 



Coldwell, C. 1972. Raven banding in Nova Scotia. Bird-Bander. 
43:288. 

Conner, R.N. , and C.S. Adkisson. 1976. Concentration of foraging 
common ravens along the Trans-Canada Highway. Can. Field-Nat. 
90:496-497. 

Conner, R.N. , I.D. Prather, and C.S. Adkisson. 1975. Common raven 
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Conner, R.N. , I.D. Prather, and J.W. Via. 1976. The raven: Symbol 
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Coombes, R.A.H. 1948. The flocking of the raven. Brit. Birds 
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Congdon, R.T. 1948. American raven nesting in houses. Auk 
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Craighead, F.C. , Jr., and J.J. Craighead. 1949. Nesting Canada geese 
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Craighead, J.J, and F.C. Craighead, Jr. 1939. A battle of wits. 
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Cushing, J.E., Jr. 1941. Winter behavior of ravens at Tomales Bay, 
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Davis, P. 1967. Raven's response to sonic bang. Brit. Birds 
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DeArmond, D.B. 1975. Raven. Alaska NW Publ. Co., Anchorage. 

Decker, F.R. 1931. Prairie falcon's nest. Oologist 48:96. 

Decker, F.R. , and J.H. Bowles. 1930. The prairie falcon in the state 
of Washington. Auk 47:27-31. 

DeVos, A. 1964. Range changes of birds in the Great Lakes region. 
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Dickey, S.S 1915. The northern raven. Oologist 32:106-107. 

Dimmick, R.W. 1968. Canada geese of Jackson Hole, their ecology and 
management. Wyo. Game Fish Comm. Bull. No. 11. 

Dorn, J.L. 1972. The common raven in Jackson Hole, Wyoming. M.S. 
thesis, Univ. Wyoming, Laramie. 



55 



Dunstan, T.C. 1976. Activity, hunting patterns, territoriality, and 
social interactions of birds of prey rn the Snake River Birds of 
Prey Natural Area, Idaho. Pages 63-131 in Snake River Birds of 
Prey Research Project, annual report, 1976, BLM, Boise. 

Elliot, R.D. 1977. Hanging behavior in common ravens. Auk 
94:777-778. 

Eustis, O.B. 1978. Common raven nesting in Alpena County. Jack-Pine 
Warbler 56:45. 

Ferguson, D. , J. Hall, M. McDermid, L. Nelson, P. Rubin, and M. 

Trimble. 1976. Birds and human structures in the Oregon desert. 
Pac. Search 11:10-11. 

Ficken, M.S. 1977. Avian play. Auk 94:573-582. 

Feilden, H.W. 1909. Ravens as scavengers. Br. Birds 3:57-58. 

Goodwin, D. 1976. Crows of the world. Cornell Univ. Press, Cornell. 

Gwinner, E. 1964. Untersuchungen uber das Ausdrucks-und 

Sozialverhalten des Kolkraben (Corvus corax L.). X. Tierpsychol. 
21:657-748. 

Gwinner, E. 1965. Beobachtungen uber Nestbau and Brutpflege des 
Kolkraben in Gefangenschaf t. J. Ornithol. 106:145-178. 

Harlow, R.C. 1922. The breeding habits of the northern raven in 
Pennsylvania. Auk 39:399-410. 

Harlow, R.F., R.G. Hooper, D.R. Chamberlain, and H.S. Crawford. 1975. 
Some winter and nesting season foods of the common raven in 
Virginia. Auk 92:298-306. 

Harrington, F.H. 1978. Ravens attracted to wolf howling. Condor 
80:236-237. 

Hewson, R. 1949. Gathering of ravens. Brit. Birds 42:181. 

Hewson, R. 1957. Social flying of ravens. Brit. Birds 50:432-434. 

Hoffmann, R. 1920. A raven pellet. Auk 37:453-454. 

Holyoak, D. 1967. Breeding biology of the Corvidae. Bird Study 
14:153-168. 

Hooper, R.G. 1973. Raven haven. Virginia Wildl. 34:6-7. 

Hooper, R.G. 1977. Nesting habitat of common ravens in Virginia. 
Wilson Bull. 89:233-242. 



56 



Hooper, R.G., H.S. Crawford, D.R. Chamberlain, and R.F. Harlow. 1975. 
Nesting density of common ravens in the Ridge-Valley region of 
Virginia. Amer. Birds 29:931-935. 

Houston, C.S. 1977. Changing patterns of Corvidae on the prairies. 
Blue Jay 35:149-155. 

Houston, D.B. 1968. The Shiras moose in Jackson Hole, Wyoming. 
Grand Teton Nat. Hist. Assoc. Tech. Bull. No. 1. 

Howard, R.P., L.O. Wilson, and F.B. Renn. 1976. Relative abundance 
of nesting raptors in southern Idaho. Raptor Res. 10:120-128. 

Howe, M.A. 1978. The changing seasons. Amer. Birds 32:968-976. 

Hurrell, A.G. 1951. Ravens using thermals. Brit. Birds 44:88-89. 

Hutson, H.P.W. 1945. Roosting procedure of Corvus corax laurence 
Hume. Ibis 87:455-459. 

Janes, S.W. 1976. The apparent use of rocks by a raven in nest 
defense. Condor 78:409. 

Jenkins, M.A. 1978. Gyrfalcon nesting behavior from hatching to 
fledging. Auk 95:122-127. 

Jollie, M. 1976. Species interrelationships of three corvids. Biol. 
58:89-111. 

Jones, F.M. 1935. Nesting of the raven in Virginia. Wilson Bull. 
47:188-191. 

Kerttu, M.E. 1973. Aging techniques for the common raven ( Corvus 

corax principalis Ridgeway). M.S. thesis, Michigan Tech. Univ., 
Houghton. 

Knowlton, G.F. 1943. Raven eats Mormon cricket eggs. Auk 60:273. 

Kochert, M.N. , A.R. Bammann, R.P. Howard, J.H. Doremus, M. DeLate, and 
D. Donahue. 1975. Reproductive performance, food habits, and 
population dynamics of raptors in the Snake River Birds of Prey 
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Project, annual report, 1975, BLM, Boise. 

Kochert, M.N. , A.R. Bammann, J.H. Doremus, M. DeLate, and J. Wyatt. 
1976. Reproductive performance, food habits, and population 
dynamics of raptors in the Snake River Birds of Prey Natural 
Area. Pages 1-57 jln Snake River Birds of Prey Research Project, 
annual report, 1976, BLM, Boise. 



57 



Kochert, M.N. , A.R. Bammann, K. Steenhof, J.H. Doremus, M. DeLate, J. 
Oakley, and T. Hamer. 1977. Reproductive performance, food 
habits, and population dynamics of raptors in the Snake River 
Birds of Prey Natural Area. Pages 1-39 ^n Snake River Birds of 
Prey Research Project, annual report, 1977, BLM, Boise. 

Larsen, K.H. , and J.H. Dietrich. 1970. Reduction of a raven 

population on lambing grounds with DRC-1339. J. Wildl. Manage. 
34:200-204. 

Lockley, R.M. 1953. Aeriol assembly of ravens in December. Brit. 
Birds 46:347-348. 

Lorenz, K. 1970. (Translated by Robert Martin) Studies in animal 
and human behaviour. Vol. 1, Harvard Univ. Press, Cambridge. 

Lucid, V.J., and R.N. Conner. 1974. A communal common raven roost in 
Virginia. Wilson Bull. 86:82-83. 

Mahringer, E.B. 1970. The population dynamics of the common raven 

( Corvus corax principalis Ridgeway) on the Baraga Plains, L'Anse, 
Michigan. M.S. thesis, Michigan Tech. Univ., Houghton. 

Mallory, F.F. 1977. An ingenious hunting behavior in the common 
raven ( Corvus corax )- Ont. Field Biol. 31:53. 

Marquiss, M. , I. Newton, and D.A. Ratcliffe. 1978. The decline of 

the raven ( Corvus corax ) in relation to afforestation in southe *n 
Scotland and northern England. J. Appl. Ecol. 15:129-144. 

McBee, C. 1937. Unusual nesting sites of the American raven. 
Oologist 44:58-59. 

McManus, R. 1935. Feeding habits of the raven in winter. Auk 52:89. 

Mech, L.D. 1970. The wolf: The ecology and behavior of an 
endangered species. Nat. Hist. Press, Garden City. 

Mishaga, R. 1974. Notes on a synchronous hatching and nesting 
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Montevecchi, W.A. 1978. Corvids using objects to displace gulls from 
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Murray, J.J. 1949. Nesting habits of the raven in Rockbridge County. 
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Mylne, C.K. 1961. Large flocks of ravens at food. Brit. Birds 
54:206-207. 

Nelson, A.L. 1934. Some early summer food preferences of the 
American raven in southeastern Oregon. Condor 36:10-15. 

58 



Oberholser, H.C. 1918. The common ravens of North America. Ohio J. 
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Parker, R.C. 1973. Prairies and people: A current look at prairie 
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Pearse, T. 1938. A remarkable influx of ravens into the Comox 
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Porter, R.D., and CM. White. 1973. The peregrine falcon in Utah, 
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Ratcliffe, D.A. 1962. Breeding density in the peregrine (Falco 
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Ratcliffe, D.A. 1970. Changes attributed to pesticides in egg 

breakage frequency and eggshell thickness in some British birds. 
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Ross, R.C. 1925. Field notes on the raven. Condor 27:172. 

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Schwan M.W. , and D.D. Williams. 1978. Temperature regulation in the 
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Smith, D.G. , and J.R. Murphy. 1973. Breeding ecology of raptors in 
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Sprunt, A. , Jr. 1956. Is the raven coming back in the Southeast? 
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Stiehl, R.B. 1978. Aspects of the ecology of the common raven in 
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Temple, S.A. 1974. Winter food habits of ravens in the Arctic Slope 
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Thompson, J.W. 1919. An unusual raven's nest. Oologist 
35:99, 103-104. 



59 



Truesdale, F. 1908. A raven's nest in a barn. Oologist 25:183-184. 

Tufts, R.W. 1916. Northern ravens in Nova Scotia. Oologist 
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Oologist 46:16-20. 

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White, CM., and T.J. Cade. 1971. Cliff-nesting raptors and ravens 
along the Colville river in Arctic Alaska. Living Bird 
10:107-150. 

White, CM., T.D. Ray, and L.W. Sowl. The 1970-1972 raptor surveys 
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Willett, G. 1941. Variation in North American ravens. Auk 
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Wolfe, M. 1977. Raptor utilization of desert habitats. Pages 82-101 
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Zirrer, F. 1945. The raven. Passenger Pigeon 7:60-67. 



60 



PHOTO CREDITS 

Frontispiece: Al Bammann 

Cover & Drawings Pages 2 and 50: Michelle LaGory 

Call, Mayo W. : Figs. 2 (upper), 3 (upper left and lower right) 

Fisher, Duane H. , Jr. : Fig. 2A (both) 

Howard, Richard : Fig. 3 (upper right) 

Knight, Richard : Fig. 3 (lower left), 3A (both) 

Unknown: Fig. 2 (lower) 



Bureau of Land Management 

Library 

50, Denver Federal Center 

Iver, CO 80225 



A-U.S. GOVERNMENT PRINTING OFFICE: 1980-0-679-9 9 1/6 1 









1 






ai Center 
Denver, CO 8G225 




o 

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I